UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


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SOUTHERN  BRANCH, 

UNIVERSITY  OF  CALIFORNIA, 

LIBRARY, 

LOS  ANGELES,  CALIF. 


WORKS   OF 

PROF.  HENRY  FAY 

PUBLISHED   BY 

JOHN  WILEY   &  SONS,  Inc. 


Microscopic  Examination  of  Steel. 

iv+8z  pages,  6  by  9,  many  plates.    Cloth,  $1.50  net. 

An  Advanced  Course  in  Quantitative  Analysis  with  Explana- 
tory Notes. 

v+ui  pages,  6  by  9.    Cloth,  $1.50  net. 


An  Advanced  Course 


IN 


Quantitative  Analysis 


WITH 


Explanatory  Notes 


HENRY  FAY,  Ph.D.,  D.Sc. 

Professor  of  Analytical  Chemistry  and  Metallography  in  the  Massachusetts 
Institute  of  Technology 


SECOND  EDITION  REVISED 


NEW  YORK 

JOHN  WILEY  &  SONS,  INC. 

LONDON:   CHAPMAN  &  HALL,  LIMITED 
1922 

49108 


COPYRIGHT,  1917,  1922, 

BY 
HENRY  FAY 


Stanhope  preos 

F.    H.GILSON   COMPANT 
BOSTON,  U.S.A. 


rot 


PREFACE  TO  SECOND  EDITION 

IN  offering  a  new  edition  every  effort  has  been  made  to  so  correct 

the  text  in  detail  as  to  make  it  more  certain  for  the  student  to  get 

I       accurate  results.    The  only  additions  have  been  in  the  "Analysis 

|       of  Duralumin"  which  has  been  selected  not  only  on  account  of 

3       its  importance  as  a  type  of  aluminum  alloys  but  because  of  the 

opportunity  to  introduce  some  new  principles. 

Much  consideration  has  been  given  to  the  various  electrometric 
^      methods  and  it  has  been  a  great  temptation  to  introduce  them 
t       but  they  were  omitted  on  account  of  their  highly  specialized  nature 
and  the  desire  to  keep  the  volume  small. 

The  author  wishes  to  express  his  appreciation  of  the  help  re- 
ceived from  his  associates  of  the  Division  of  Analytical  Chemistry. 

HENRY  FAY. 
September,  1922. 


iii 


PREFACE  TO  FIRST  EDITION 


THIS  book  is  intended  primarily  for  students  of  the  Massachu- 
setts Institute  of  Technology,  and  represents  the  work  planned  for 
those  who  have  finished  the  excellent  introductory  course  in 
"Quantitative  Analysis"  by  Professor  Henry  P.  Talbot.  Assump- 
tion has  been  made  that  the  student  is  familiar  with  the  use  of  the 
balance,  the  principles  of  volumetric  analysis,  and  of  stoichiometry, 
and  no  attempt  has  been  made  to  enlarge  upon  these  subjects.  The 
material  offered  is  chosen  to  illustrate  principles  and  to  train  the 
student  in  manipulation.  In  certain  cases  a  student  is  offered  a 
choice  of  method,  as  in  the  determination  of  sulphur  in  pyrite,  and 
in  other  cases  where  the  principle  differs,  as  in  the  determination 
of  manganese  in  steel,  it  is  desirable  that  the  student  acquaint 
himself  with  each  method. 

The  student  is  earnestly  requested  to  read  and  understand  each 
method  before  beginning  any  laboratory  work.  Adequate  prepa- 
ration of  apparatus  should  also  be  made. 

In  preparing  this  volume  the  author  wishes  to  express  his  appre- 
ciation of  the  helpful  suggestions  of  Professor  R.  S.  Williams,  and 
of  the  kindly  services  of  Mr.  L.  F.  Hamilton. 

HENRY  FAY. 

MASSACHUSETTS  INSTITUTE  OF  TECHNOLOGY, 
May,  1917. 


CONTENTS 


PART  I 

MINERAL  ANALYSIS 

PAGE 
SAMPLING  FOR  ANALYSIS i 

DETERMINATION  OF  SILICA  IN  SILICATES 4 

Decomposable  Silicate  (Laumontite) 

Refractory  Silicate  (Feldspar) 
DETERMINATION  OF  POTASSIUM  AND  SODIUM  IN  SILICATES 9 

J.  Lawrence  Smith  Method. 

Perchloric  Acid  Method. 
ANALYSIS  OF  SPATHIC  IRON  ORE 15 

Determination  of  Iron,  Aluminum,  Manganese,  Calcium,  and  Magnesium. 
DETERMINATION  OF  SULPHUR  IN  PYRITE 29 

Lunge    Method;    Allen    and    Bishop    Method;    Fresenius    Method; 

Sodium  Peroxide  Method. 
DETERMINATION  OF  TITANIUM  IN  TITANIUM  IRON  ORE 39 

Method  of  Gooch;  Method  of  Barneby  and  Isham. 
IODOMETRIC  DETERMINATION  OF  COPPER 43  ]/ 

Method  of  Low. 
PROXIMATE  ANALYSIS  OF  COAL  ....    47 

Determination  of  Moisture,  Ash,  Volatile  Matter,  Fixed  Carbon, 
Sulphur. 

PART  II 
METAL  ANALYSIS 

ANALYSIS  OF  PHOSPHOR-BRONZE 50  / 

Determination  of  Copper,  Lead,  Tin,  Phosphorus. 
DETERMINATION  OF  CARBON  IN  STEEL 59 

Direct  Combustion  Method. 
DETERMINATION  OF  MANGANESE  IN  STEEL 65 

Volhard  Method;  Williams  Method;  Bismuthate  Method. 
DETERMINATION  OF  PHOSPHORUS  IN  IRON  AND  STEEL 75  / 

Reduction  Method;    Alkalimetric  Method. 
DETERMINATION  OF  SULPHUR  IN  STEEL 83 

Evolution  Method. 

vii 


viii  CONTENTS 

PAGE 

DETERMINATION  OF  SULPHUR  IN  CAST  IRON 87 

Bamber  Method. 

DETERMINATION  OF  SILICON  m  CAST  IRON 89 

Drown  Method. 

DETERMINATION  OF  COPPER  IN  STEEL 91 

DETERMINATION  OF  NICKEL  nsr  STEEL 92 

•  Brunck's  Method. 

DETERMINATION  OF  CHROMIUM  IN  STEEL 94 

Barba  Method;  Cain  Method. 

DETERMINATION  OF  TUNGSTEN  IN  STEEL 98 

DETERMINATION  OF  VANADIUM  IN  STEEL 100 

ANALYSIS  OF  DURALUMIN 103 

LOGARITHM  TABLES 108 

TABLE  OF  ATOMIC  WEIGHTS 112 


QUANTITATIVE  ANALYSIS 


SAMPLING  FOR  ANALYSIS 

THE  selection  and  preparation  of  a  sample  for  analysis, 
whether  it  be  an  ore,  rock,  mineral,  or  metal,  is  just  as  im- 
portant as  the  method  of  analysis  itself.  In  a  brief  dis- 
cussion of  the  subject  it  is  very  difficult  to  lay  down  general 
rules  for  making  the  samples  owing  to  the  varying  con- 
ditions, such  as  size  of  shipment,  or  the  character  of  the  ore 
or  metal.  The  desired  end  is  to  obtain  a  sample  which  will 
be  representative  of  a  whole  shipment,  whether  it  be  a  car 
load,  a  train  load,  a  cargo,  or  a  large  or  small  shipment  of 
metals  in  their  varied  forms.  Many  of  the  controversies 
between  producer  and  consumer  may  be  traced  to  inequality 
of  sample.  The  sampling  by  the  producer  and  consumer 
in  the  case  of  ores  is  done  usually  under  very  different  con- 
ditions and  it  is  quite  remarkable  that  there  should  be  such 
close  agreement  rather  than  that  there  should  be  much 
divergence. 

Inasmuch  as  the  principle  of  mineral  or  rock  sampling  is 
in  general  the  same,  the  sampling  of  a  car  of  ore  will  be 
taken  as  typical.  Immediately  on  receipt  of  the  car,  samples 
should  be  taken  by  means  of  a  small  shovel  or  trowel  from 
various  parts  of  the  car.  The  best  method  of  getting  even 
distribution  is  to  take  a  one-  or  two-pound  sample  from  a 
large  number  of  places,  the  car  being  divided  so  as  to  obtain 
the  samples  at  equal  distances  from  the  centre  and  ends,  as 
well  as  between;  or  the  car  may  be  sampled  along  a  zig-zag 
line  running  from  one  corner  to  the  diagonally  opposite  corner, 
crossing  the  car  at  one- third  and  two- thirds  of  the  length. 
This  method  must  be  followed  not  only  at  the  surface  of  the 
car,  but  also  midway  between  top  and  bottom  and  near  the 


2  QUANTITATIVE  ANALYSIS 

bottom  of  the  car.  When  lumps  are  encountered,  small 
portions  of  each  lump  must  be  chipped  off  and  an  equal 
portion  of  fine  must  be  taken  adjacent  to  the  lump. 

The  total  sample  is  then  mixed,  piled  in  a  cone  and  alternate 
quarters  rejected.  The  material  thus  obtained  is  further 
subdivided  by  crushing  or  grinding,  and  again  coned  and 
quartered,  and  this  process  continued  until  a  one-  or  two- 
pound  sample  which  will  pass  through  a  loo-mesh  sieve  is 
obtained.  In  rock  or  mineral  sampling,  it  is  absolutely 
necessary  to  crush  or  grind  all  of  the  quarters  taken  and  not 
to  reject  any  portion  on  account  of  extreme  hardness  or 
softness.  This  would  defeat  the  end  which  is  aimed  at. 

Precaution  should  also  be  taken  when  removing  a  sample 
from  the  general  supply  bottle  as  there  is  strong  tendency 
for  the  coarser  particles  to  find  their  way  to  the  bottom  of 
the  container.  The  bottle  should  be  well  shaken,  or  prefer- 
ably rotated  on  a  wheel,  or  the  contents  spread  out  and  mixed 
on  a  large  piece  of  glazed  paper.  Unexpected  variations  may 
arise  from  year  to  year  from  neglect  of  this  precaution. 

The  sampling  of  ores  is  made  difficult  by  the  uneven  char- 
acter of  coarse  and  fine,  hard  and  soft,  material,  and  of  minerals 
of  high  and  low  specific  gravity.  The  degree  of  fineness  to 
which  a  mineral  or  ore  is  ground  is  also  an  important  factor. 
Many  analyses  are  affected  due  to  failure  to  take  this  fact 
into  consideration.  In  the  determination  of  water,  sulphur 
in  pyrite,  or  ferrous  Iron  in  silicates  large  variations  may 
occur  between  different  analysts  because  of  the  differences  in 
the  fineness  of  the  samples  used.  In  fine  grinding  oxidation 
of  sulphur  or  iron  may  occur,  or  there  may  be  loss  of  water. 
It  is  advisable  in  such  cases  to  make  determinations  on  both 
fine  and  coarse  material. 

The  difficulty  of  sampling  metals  is  principally  due  to  the 
tendency  to  segregation  in  the  ingot,  or  cast  form.  This 
tendency  is  due  to  the  fact  that  during  solidification  selec- 
tive crystallization  takes  place  and  thus  produces  a  melt 
richer  in  one  or  more  constituents  which  solidify  at  a  lower 
temperature.  When  a  metal  passes  from  the  liquid  to  the 


SAMPLING   FOR   ANALYSIS  3 

solid  state,  the  outside  skin  solidifies  first  on  account  of  the 
more  rapid  conduction  of  heat  from  the  surface,  and  thus 
leaves  a  molten  interior.  This  molten  mass  gives  up  crystals 
to  those  already  formed  and  there  is  a  constant  enriching  of 
the  material  in  the  melt.  In  steel,  carbide  and  phosphide 
of  iron  are  thus  concentrated  and  are  always  segregated 
in  that  portion  of  an  ingot  last  to  solidify,  viz.:  in  the  upper 
central  portion  of  the  ingot. 

Again,  compounds  of  lower  or  higher  specific  gravity  than 
the  main  mass  of  the  melt  may  form  and  thus  rise  or  fall  in 
the  still  molten  mass.  A  good  example  of  this  type  of  segre- 
gation is  in  the  case  of  sulphur  in  steel  which  is  always  com- 
bined with  manganese  as  manganese  sulphide  and  being  of 
lower  specific  gravity  than  the  steel  itself  rises  to  the  surface 
of  the  melt. 

Due  regard  to  segregation  must  be  made  in  the  sampling  of 
any  cast  metal.  In  products  which  are  forged  from  the  ingot 
the  segregation  persists  in  the  forged  material  irrespective  of 
shape.  Rigid  specifications  for  steel  usually  call  for  the  rejection 
of  definite  portions  of  the  top  (usually  25  per  cent)  and  bottom 
(usually  5  per  cent)  of  the  ingot,  but  even  in  spite  of  these 
precautions,  differences  are  invariably  found.  It  is  never 
safe  to  assume  that  any  metal  is  uniform  and  it  is  much  better 
to  assume  that  it  lacks  uniformity  and  proceed  accordingly. 

In  the  sampling  of  a  steel  rail,  for  instance,  it  would  be 
foolish  to  assume  that  a  single  sample  would  represent  the 
whole  unless  that  single  sample  were  obtained  by  boring  a 
hole  entirely  through  the  rail  from  top  to  bottom.  Even  so 
this  method  would  not  be  so  satisfactory  as  taking  samples 
from  a  number  of  holes  distributed  over  the  head,  foot,  and 
web,  or  better  by  planing  over  the  whole  surface.  In  all 
cases,  as  much  of  the  surface  as  possible  should  be  represented 
in  the  sample. 

If  possible,  a  macroscopic  survey  should  be  made  before 
sampling  any  steel  if  the  material  is  likely  to  be  a  subject  of 
controversy.  To  this  end,  a  cross  section  of  the  piece  is  fairly 
smoothly  polished  and  then  etched  either  with  an  8  per  cent 


4  QUANTITATIVE  ANALYSIS 

solution  of  copper  ammonium  chloride 1  or  a  6  per  cent  solution 
of  iodine  in  alcohol.  In  the  former  case  segregated  carbide 
and  phosphide  appear  darker  than  the  surrounding  metal,  and 
in  the  latter  case  phosphide  in  particular  appears  lighter 
colored.  Interpretation  of  results  thus  obtained  should  always 
be  left  to  those  experienced  in  this  work. 

It  is  needless  to  add  that  the  tool  with  which  metal  samples 
are  taken  should  be  free  from  oil. 

DETERMINATION  OF  SILICA  IN  A  DECOMPOSABLE 
SILICATE 

LAUMONTITE 

Weigh  approximately  0.5  gram  of  the  finely  ground  material 
into  a  300  cc.  porcelain  casserole.  Add  about  25  cc.  of  water, 
and  stir  until  the  silicate  is  completely  wet.  Now  add  in 
small  portions  25  cc.  hydrochloric  acid  (sp.  gr.  1.12),  heating 
the  casserole  and  stirring  the  contents  during  the  addition  of 
the  acid,  and  continuing  the  heating  until  the  silicate  is  com- 
pletely decomposed  or  until  no  gritty  residue  is  left.  Evapo- 
rate the  solution  to  dryness,  stirring  frequently  if  there  is  any 
tendency  toward  the  formation  of  a  jelly-like  mass.  When 
completely  dry,  add  just  enough  concentrated  hydrochloric 
acid  to  moisten  the  residue,  and  evaporate  again.  Moisten 
the  residue  again  with  concentrated  hydrochloric  acid,  warm 
gently,  then  dilute  with  200  cc.  of  water,  and  heat  to  boiling. 
Filter  off  the  silica  as  soon  as  it  settles,  without  attempting 
to  remove  that  which  adheres  to  the  wall  of  the  casserole,  and 
wash  with  hot  dilute  hydrochloric  acid  (one  part  acid,  sp.  gr. 
1. 1 2,  to  three  parts  water)  until  the  filter  paper  is  free  from 
iron  stain.  Finish  the  washing  with  hot  water,  and  wash 
until  free  from  chlorides. 

Evaporate  the  filtrate  and  washings  to  dryness  in  the  same 
casserole,  and  treat  exactly  as  in  the  first  evaporation,  receiv- 
ing the  recovered  silica  on  a  second  filter  paper,  and  removing 
the  silica  adhering  to  the  walls  of  the  casserole  by  means  of 

1  Heyn.  International  Soc.  for  Testing  Materials,  Brussels  Congress,  1906. 


DETERMINATION  OF  SILICA  5 

a  rubber  "policeman."  Wash  as  before,  and  then  transfer 
the  partially  dried  filter  papers  to  a  weighed  platinum  crucible. 
Place  the  crucible  on  its  side  and,  by  means  of  a  low  flame 
placed  under  the  front  of  the  crucible,  smoke  off  the  paper  at 
a  low  heat.  When  the  volatile  products  are  removed,  place 
the  full  oxidizing  flame  of  the  Tirrill  burner  at  the  rear  of  the 
crucible,  and  heat  until  the  residue  is  white.  Finish  the 
ignition,  with  the  crucible  covered,  over  a  Meker  burner  or 
blast  lamp,  and  heat  to  constant  weight. 

When  constant  weight  has  been  obtained,  add  to  the  cru- 
cible one  or  two  drops  of  v/ater,  and  then  3  to  4  cc.  of  hydro- 
fluoric acid.  Add  one  or  two  drops  of  dilute  sulphuric  acid, 
and  heat  gently  in  a  hood  with  good  draught,  until  all  of  the 
silica  has  volatilized.  If  there  is  considerable  residue  it  may 
be  necessary  to  repeat  the  treatment  with  hydrofluoric  acid. 
When  all  of  the  silica  has  volatilized,  heat  over  the  Tirrill 
burner,  and  finally  over  a  Meker  burner  or  blast  lamp  for  a 
few  minutes.  The  loss  in  weight  represents  the  amount  of 
SiC>2  present. 

DETERMINATION  OF  SILICA  IN  A  REFRACTORY 
SILICATE 

PELDSPAR 

Mix  thoroughly  in  a  platinum  crucible  approximately  0.50 
gram  of  finely  ground  feldspar  with  about  six  times  its  weight 
of  pure,  dry  sodium  carbonate.  Place  the  covered  crucible 
over  a  small  flame  and  gradually  raise  the  flame  to  full  heat 
and  continue  heating  for  20-30  minutes,  or  until  effervescence 
has  ceased.  Now  place  the  crucible  in  the  oxidizing  flame  of 
a  Meker  burner  or  blast  lamp,  directing  the  flame  at  an  angle, 
if  the  blast  lamp  is  used,  against  the  side  and  bottom  of  the 
crucible,  and  continue  heating  for  five  minutes.  At  the  end 
of  this  time  shut  off  the  gas  supply  suddenly  and  allow  the  air 
blast  to  play  upon  the  covered  crucible  until  cool.  Place  the 
crucible  top  side  down  in  a  porcelain  casserole  and  gently  tap 
until  the  solidified  mass  is  removed.  If  the  Meker  burner  is 


6  QUANTITATIVE  ANALYSIS 

used  the  best  method  of  removing  the  melt  is  to  insert  into  the 
molten  mass  the  coiled  end  of  a  platinum  wire  and  allow  the 
mass  to  solidify  around  the  wire.  When  cool,  reheat  gently 
with  a  small  flame  so  as  to  soften  the  edges  and  at  the  same 
time  put  the  wire  under  tension.  If  properly  done  this  should 
remove  the  melt  as  a  whole.  Wash  with  hot  water  the  material 
adhering  to  the  cover  and  crucible  into  the  casserole  and  then 
proceed  with  the  decomposition  and  determination  of  the  silica 
exactly  as  described  in  the  preceding  method. 

Notes.  —  i.  The  ease  with  which  any  silicate  is  decomposed 
is  determined  by  the  ratio  of  base  to  acid.  In  the  more  basic 
silicates,  hydrochloric  acid  will  decompose  them  readily.  Such 
silicates  are  referred  to  as  soluble  or  decomposable.  With 
increase  in  the  ratio  of  silica  to  base  the  decomposition  with 
acids  takes  place  less  readily,  and  when  the  silicate  is  distinctly 
acidic  in  character  there  is  little,  if  any,  action  by  dilute  acids. 
The  latter  type  of  silicate  is  called  refractory,  or  undecompos- 
able.  Such  silicates  may,  however,  be  rendered  decomposable 
by  converting  them  into  basic  silicates  by  fusion  with  sodium 
carbonate,  lead  oxide,  or  other  similar  basic  compounds.  In 
this  way  the  proportion  of  base  to  silica  is  so  raised  as  to  make 
them  easily  decomposable  by  dilute  acids. 

Most  of  the  artificial  silicates,  such  as  the  various  metal- 
lurgical slags,  Portland  cement,  etc.,  are  decomposable. 

Certain  silicates  occurring  as  minerals  are  insoluble  in  their 
natural  state,  but,  when  brought  to  the  fusion  temperature, 
are  converted,  after  cooling,  without  change  of  composition, 
into  soluble  silicates. 

2.  When  strong  acid  is  brought  in  contact  with  decompos- 
able silicates  silicic  acid  is  separated  in  gelatinous  form  which 
encloses  particles  of  undecomposed  silicate.  On  evaporation 
this  jelly-like  mass  dries  around  the  unattacked  particles  and 
protects  them  from  the  action  of  the  acid.  In  order  to  avoid 
this  difficulty,  the  silicate  is  first  moistened  with  water,  and 
small  amounts  of  acid  are  added  from  time  to  time  so  as  not  to 
have  it  in  excess  until  after  the  decomposition  has  taken  place. 
By  the  cautious  addition  of  acid  the  whole  of  the  silicate  may 
be  brought  into  solution  and  no  silica  will  separate  until  the 
solution  has  been  concentrated  somewhat. 


DETERMINATION  OF  SILICA  7 

Stirring  and  breaking  up  of  the  jelly,  when  once  formed,  aids 
the  evaporation  and  also  prevents  spattering. 

3.  The  recovery  of  silica  by  a  second  evaporation  after  the 
filtration  of  the  major  portion  seems  to  be  absolutely  neces- 
sary.    Formerly  it  was  the  custom  to  recover  the  silica  passing 
into  the  nitrate  after  a  single  evaporation  by  evaporating  the 
precipitate  of  iron  and  alumina  produced  by  ammonia  with 
either  hydrochloric  or  sulphuric  acids,  or  to  correct  the  ignited 
oxides  of  iron  and  alumina  for  silica  by  fusion  with  potassium 
pyrosulphate.     The  double  evaporation  method,  with  inter- 
vening nitration,  seems  to  be  more  efficient  and  less  cumber- 
some. 

The  necessity  of  the  recovery  of  the  silica  passing  into  the 
filtrate  after  a  single  evaporation  was  early  recognized  by 
Bunsen,1  later  by  Ludwig,2  and  by  Meineke,3  and  more  re- 
cently by  Cameron,4  and  Hillebrand.5 

Invariably  small  amounts  are  recovered  by  the  second 
evaporation,  and  consequently  the  operation  should  never 
be  neglected.  This  process  has  the  distinct  advantage  over 
other  methods  in  that  no  silica  is  introduced  through  the  use  of 
ammonia,  which  always  carries  from  small  to  large  amounts. 

4.  The  temperature  of  drying  the  siliceous  residue  has  been 
the  subject  of  considerable  investigation  and  much  difference 
of  opinion. 

According  to  the  work  of  Gilbert 6  and  of  Hillebrand,7  dry- 
ing temperatures  above  that  of  the  steam  bath  have  little 
advantage  and  are  sometimes  the  cause  of  considerable  silica 
going  into  the  filtrate  on  account  of  recombination  of  silica 
at  the  higher  temperatures.  Furthermore,  silica  so  obtained 
frequently  contains  large  amounts  of  impurity.  Blount 8 
recommends  a  temperature  of  200°  for  the  determination  of 
silica  in  Portland  cement,  but  this  is  advisable  only  hi  certain 
special  cases  and  should  not  be  adopted  for  general  work. 

Am.  Chem.  Pharm.,  61,  265. 

Z.  anal.  Chem.,  9,  321. 

Repert.  anal.  Chem.,  7,  215. 

Chem.  News,  69,  171. 

Bulletin  422,  U.  S.  Geol.  Survey,  p.  91. 

Tech.  Quart.,  3,  61. 

/.  Am.  Chem.  Soc.,  24,  262. 

/.  Soc.  Chem.  Ind.,  21,  1217. 


QUANTITATIVE  ANALYSIS 

5.  The  final  temperature  of  ignition  for- silica,  as  well  as  for 
other  oxides,  such  as  A^Os,  Fe2O3,  TiO2,  Sn02,  etc.,  must 
be  high.     It  is  claimed  by  many  investigators  that  this  heat 
is  necessary  to  deprive  the  silica  of  the  last  traces  of  water, 
although  the  evidence  is  not  conclusive  that  moisture  alone  is 
the  cause  of  variation  in  weight.     It  has  been  shown  by  experi- 
ments conducted  in  this  laboratory  that  in  many  cases  sodium 
or  potassium  salts  are  the  cause  and  that  it  is  necessary  to 
have  a  prolonged  high  temperature  to  remove  the  traces  of 
alkali  which  had  been  occluded  by  the  silica. 

When  igniting  to  constant  weight,  it  must  not  be  forgotten 
that  some  platinum  crucibles  lose  weight  steadily,  and  the  rate 
of  loss  should  therefore  be  determined  for  such  a  crucible. 

6.  Silica,  as  determined  by  evaporation  to  dryness,  is  never 
absolutely  pure,  but  is  always  contaminated  by  traces  of 
aluminum,  iron,  calcium,  or  magnesium.     The  weight  must 
always  be  corrected  by  volatilizing  the  silica  as  fluoride  and 
weighing  the  residue  after  heating  as  before.    This  residue, 
although  frequently  small,  should  never  be  neglected. 

7.  Sodium    carbonate    is    invariably    contaminated    with 
silica  and  other  impurities.     For  analytical  purposes  it  should 
either  be  purified  by  recrystallization,  or  the  amounts  of  silica, 
etc.,  should  be  carefully  determined.     One  should  never  be 
deceived  by  a  label  and  should  prove  to  his  own  satisfaction 
the  presence  or  absence  of  impurities.    If  a  sample  of  pure 
sodium  carbonate  be  prepared  or  the  amount  of  silica  be  de- 
termined, such  a  sample  should  be  carefully  guarded  and  used 
only  for  silicate  analyses. 

Sodium  bicarbonate  has  been  recommended  as  a  flux  and 
has  much  to  commend  its  use,  but  it  is  very  seldom  employed. 

8.  Lead  oxide,1  bismuth  oxide,2  and  boric  oxide 3  have  been 
proposed  for  the  decomposition  of  refractory  silicates.     By 
the  use  of  these  substances  there  is  not  only  the  distinct  ad- 
vantage that  all  of  the  flux  may  be  removed  —  lead  and  bis- 
muth by  means  of  hydrogen  sulphide,  and  boron  by  means  of 
methyl  alcohol  —  thus  preventing  adhesion  of  sodium  salts, 
but  sodium  and  potassium  may  be  determined  in  the 

1  Berthier,  Ann.  de  Chim.  el  de  Phys.  (2),  17,  28. 

1  Hempel,  Z.  anal.  Chem.,  20,  496. 

*  Jannasch  and  Heidenreich,  Z.  anorg.  Chem.,  12,  208. 


DETERMINATION  OF  POTASSIUM    AND   SODIUM  9 

sample.  These  methods  have  much  to  commend  them,  but 
they  have  not  been  extensively  used.  The  principal  objection 
to  the  first  two  is  the  easy  reducibility  of  lead  and  bismuth 
either  by  the  reducing  flame  of  the  burner  or  by  the  presence 
of  organic  matter.  This  objection  is  not  valid  if  ordinary 
precautions  are  taken. 

Hillebrand  has  urged  two  objections  against  the  boric  oxide 
method,  viz.:  the  deposition  of  boric  acid  due  to  the  hydrolysis 
of  the  volatile  boric  ether,  and  the  use  of  the  oxygen  flame  when 
the  alkalis  are  to  be  determined.  Another  very  important 
objection  is  the  difficulty  in  preparing  the  flux  in  pure  and 
finely  divided  condition.  Fused  boric  oxide  is  almost  as 
difficult  to  handle  as  some  of  the  hardest  minerals. 

9.  It  is  evident  that  the  methods  given  are  not  applicable 
to  the  determination  of  silica  in  minerals  which  also  contain 
fluorine.  For  a  method  consult  Bulletin  700,  U.  S.  Geological 
Survey. 

DETERMINATION  OF  POTASSIUM  AND  SODIUM  IN 
SILICATES 

METHOD   OF  J.   LAWRENCE   SMITH 

Weigh  into  a  clean,  dry,  porcelain  mortar  0.5-1.0  gram 
of  finely  ground  feldspar.  Weigh  an  equal  quantity  of  dry 
ammonium  chloride  into  the  mortar.  Place  the  mortar  on  a 
piece  of  glazed  paper  and  grind  together  thoroughly  with  the 
pestle  until  the  feldspar  and  ammonium  chloride  are  thoroughly 
mixed.  Weigh  out  eight  parts  of  calcium  carbonate,  free  from 
alkali,  and  transfer  gradually  about  three-quarters  of  this 
amount  to  the  mortar,  mixing  it  with  the  feldspar.  Transfer 
the  mixture  to  a  platinum  crucible,  and  use  the  remaining 
carbonate  to  clean  out  the  mortar,  placing  this  on  top  of 
the  main  portion,  as  a  cover.  Place  the  lid  on  the  crucible, 
and  heat  so  gently  for  fifteen  minutes  that  the  ammonium 
chloride  is  not  visibly  volatilized,  but  that  the  odor  of  ammo- 
nia is  distinctly  perceptible.  Then  heat  for  forty-five  min- 
utes, so  that  the  lower  third  of  the  crucible  is  red.  The 
proper  degree  of  heat  can  be  obtained  if  the  crucible  is  placed 


10  QUANTITATIVE   ANALYSIS 

just  over  a  flame  which  has  been  lowered  to  about  three- 
quarters  of  an  inch  in  height. 

When  cool  detach  the  sintered  mass  from  the  crucible 
and  place  it  in  a  casserole.  Pour  on  it  about  150  cc.  of  hot 
water  and  allow  it  to  stand  until  the  mass  has  softened. 
Then  cautiously  crush  and  grind  until  no  lumps  remain.  Boil 
the  water  for  a  few  minutes,  allow  the  residue  to  settle,  and 
decant  through  a  filter  into  a  large  casserole.  Repeat  the 
boiling  and  decantation,  using  about  50  cc.  of  water  each 
time  until  the  wash  water  is  free  from  chlorides,  finally  throw- 
ing the  insoluble  residue  onto  the  filter  and  washing  with  hot 
water.  As  the  process  of  washing  free  from  chlorides  is  a 
tedious  one,  it  is  advisable  not  to  begin  testing  until  at  least 
500  cc.  of  wash  water  have  been  used,  and  then  by  using  very 
small  quantities  and  comparing  with  a  blank  containing  the 
same  quantity  of  reagents. 

Add  to  the  filtrate  a  slight  excess  of  ammonium  carbonate 
solution,  a  drop  or  two  of  ammonia,  and  then  concentrate  to 
about  100  cc. 

Filter  the  calcium  carbonate  on  a  small  filter  paper,  and 
receive  the  filtrate  and  washings  in  a  platinum  dish.  Evapo- 
rate the  solution  to  dryness,  and  then  cautiously  expel  the 
ammonium  salts,  taking  care  not  to  allow  the  bottom  of  the 
dish  to  become  red.  When  cool  dissolve  in  a  small  quantity 
of  water,  add  one  or  two  drops  of  ammonia,  and  ammonium 
oxalate  drop  by  drop  until  no  further  precipitation  takes  place. 
Digest  on  a  water  bath  for  a  quarter  of  an  hour,  and  again 
filter  through  a  small  filter.  Evaporate  the  filtrate  to  dryness, 
and  again  cautiously  ignite  to  remove  ammonium  salts. 

The  residue,  which  should  be  nearly  white,  is  ready  for 
weighing  after  drying  in  a  desiccator.  It  shouM  consist  of  the 
chlorides  of  sodium  and  potassium,  unless  lithium  is  present. 

To  separate  the  sodium  and  potassium  proceed  as  follows: 
Dissolve  the  weighed  residue  in  a  small  quantity  of  water. 
The  solution  should  show  no  evidence  of  insoluble  matter. 
Add  one  or  two  drops  of  hydrochloric  acid  (sp.  gr.  1.12) 
and  about  one  and  one-half  times  the  calculated  amount  of 


DETERMINATION  OF  POTASSIUM  AND   SODIUM  II 

hydrochlorplatinic  acid,  assuming  the  total  weight  of  chlorides 
to  be  sodium  chloride.  Evaporate  the  solution  over  a  beaker 
of  hot  water,  taking  care  not  to  allow  the  water  to  boil.  The 
evaporation  should  continue  until  a  crystallized  crust  has 
formed  over  the  surface  and  only  i  or  2  cc.  of  solution  are 
left.  When  removed  from  the  water  bath  the  whole  mass 
should  be  dry.  Cover  the  residue  with  a  liberal  amount  of 
absolute  alcohol,  crush  the  salts  with  a  glass  rod,  and  stir  at 
frequent  intervals  for  a  half  hour.  Decant  the  liquid  through 
a  weighed  Gooch  crucible,  wash  thoroughly  with  alcohol  until 
the  washings  run  through  colorless,  and  a  drop  evaporated  on 
a  piece  of  clean  platinum  leaves  no  residue.  Dry  to  constant 
weight  at  110°. 

The  precipitate  should  consist  of  a  heavy  yellow  powder 
composed  of  octahedral  crystals,  having  the  composition  rep- 
resented by  the  formula  K2PtCl6.  It  should  be  entirely  free 
from  the  orange-colored  sodium  salt  NasPtCle^H^O,  and  from 
crystals  of  sodium  chloride. 

Notes.  —  i.  The  reaction  upon  which  the  method  is  founded 
may  be  represented  as  follows: 

aKAlSisOs  +  6CaCO3  +  2NH4C1  = 

6CaSiO3  +  6CO2  +  A12O3  +  2KC1  +  2NH3  +  H2O. 

In  addition  to  this  reaction  there  is  also,  of  course,  con- 
siderable decomposition  of  the  calcium  carbonate  to  calcium 
oxide  and  some  formation  of  calcium  chloride,  both  of.  which 
appear  in  the  nitrate  in  the  water  extract.  The  completeness 
of  the  reaction  is  dependent  upon  the  fineness  of  the  sample 
and  the  care  exercised  in  mixing  the  sample  with  ammonium 
chloride.  The  heat  necessary  to  complete  the  reaction  is  not 
great,  if  sufficient  care  has  been  taken  to  have  a  finely  ground 
sample;  but  it  is  preferable,  if  possible,  in  order  to  ensure 
complete  decomposition,  to  use  the  long  platinum  crucible, 
closed  by  a  cap,  as  recommended  by  J.  Lawrence  Smith. 

In  case  the  silicate  contains  much  ferrous  iron,  the  mass, 
instead  of  sintering,  will  fuse  to  a  hard  cake.  In  cases  of 
this  kind  it  is  necessary  to  increase  the  amount  of  calcium 
carbonate. 

Silicates  may  also  be  decomposed  by  means  of  sulphuric 


12  QUANTITATIVE  ANALYSIS 

and  hydrofluoric  acid,  but  this  method  has  the  disadvantage 
that  it  is  necessary  to  remove  iron,  aluminum,  magnesium, 
etc.  Each  of  these  substances  may  carry  down  more  or  less 
sodium  and  potassium.  In  the  J.  Lawrence  Smith  method 
these  substances  are  removed  in  the  beginning  of  the  opera- 
tion, being  precipitated  by  the  calcium  hydroxide. 

In  case  it  is  necessary  to  remove  magnesium  from  a  solution 
in  which  sodium  and  potassium  are  to  be  determined,  it  is 
undesirable  to  use  the  phosphate  separation  on  account  of 
the  difficulty  of  the  removal  of  the  excess  of  the  reagent. 
It  is  much  better  to  convert  the  magnesium,  sodium,  and 
potassium  into  chlorides,  and  then  to  heat  with  mercuric 
oxide. 

HgO  +  MgCl2  =  MgO  +  HgCl2. 

The  excess  of  mercuric  oxide  and  mercuric  chloride  can 
be  volatilized,  and  the  potassium  and  sodium  chlorides  can  be 
separated  from  magnesium  oxide  by  means  of  water. 

The  alkalies  may  also  be  determined  when  the  silicate  is 
decomposed  by  means  of  lead  oxide,  boric  acid,  bismuth 
oxide,  etc. 

2.  One  of  the  defects  of  the  method  is  the  fact  that  the 
calcium    carbonate    invariably    contains    small    amounts    of 
alkali,  principally  the  sodium  salt;  but  by  making  a  blank 
determination  this  may  be  corrected.    The  amount  of  im- 
purity should  be  placed  on  the  label  of  the  bottle  of  cal- 
cium carbonate,  and  this  sample  should  be  preserved  for  this 
determination  only.     The  ammonium  chloride  may  be  purified 
by  sublimation. 

3.  In  addition  to  the  removal  of  the  calcium  it  may  also 
be  necessary,  in  case  the  rock  contained  sulphur,  to  remove 
small  amounts  of  sulphate.     This  would  cause  a  contamina- 
tion of  the  potassium  chlorplatinate  on  account  of  the  insolu- 
bility of  sodium  sulphate  in  alcohol.     Its  removal  may  be 
accomplished  by  the  addition  of  a  drop  or  two  of  barium 
chloride,  and  the  removal  of  the  excess  of  the  latter  by  means 
of  ammonium  carbonate. 

The  removal  of  the  calcium  by  means  of  ammonium  car- 
bonate has  the  distinct  advantage  that  the  products  of  its 
hydrolysis 

(NH4)2C03  +  2H20  ^±  2NH40H  +  H2O 


DETERMINATION  OF  POTASSIUM  AND   SODIUM  13 

are  more  or  less  completely  removed  in  the  process  of  evapo- 
ration. With  ammonium  oxalate,  however,  there  is  more  or 
less  accumulation  of  oxalic  acid,  which  upon  heating  gives 
considerable  carbonaceous  material  which  is  difficult  to  remove 
from  the  solution. 

4.  The  separation  of  potassium  from  sodium  is  based  on 
the  fact  that  potassium  chlorplatinate  is  insoluble  in  alcohol, 
while  the  sodium  chlorplatinate  and  excess  hydrochlorplatinic 
acid  are  soluble.    As  there  is  some  danger  of  hydrolysis 
of  the  potassium  chlorplatinate,  according  to  the  reaction, 

K2PtCl6  +  H20  ^±  K2PtCl5  OH  +  HC1, 

it  is  necessary  to  make  the  separation  in  the  presence  of  a 
drop  or  two  of  hydrochloric  acid  to  prevent  this.  After  the 
addition  of  hydrochlorplatinic  acid  it  is  advisable  to  protect 
the  solution  from  dust,  which  would  cause  a  partial  reduction 
to  metallic  platinum.  To  confirm  the  result  the  potassium 
chlorplatinate  may  be  reduced  by  heating  with  dry  oxalic 
acid,  and  the  metallic  platinum  may  be  weighed,  or  the 
chlorine  in  the  potassium  chloride  may  be  determined.  The 
reaction  taking  place  is  shown  in  the  equation, 
K2PtCl6  +  (COOH)2  =  2KC1  +  Pt  + 
2HC1  +  2C02  +  C12. 

This  method  may  also  be  applied  to  the  nitrate  containing  the 
sodium,  finally  converting  the  sodium  into  sodium  sulphate. 

5.  Instead  of  weighing  the  potassium  chlorplatinate  on  a 
Gooch  crucible  it  may  be  filtered  on  paper,  washed  in  the 
usual  way  with  alcohol,  and  after  the  washing  is  complete 
it  may  be  dissolved  in  hot  water  and  the  solution  allowed 
to  run  into  a  weighed  platinum  dish.    After  evaporation  to 
dryness  this  may  be  weighed. 

In  all  cases  precaution  must  be  taken  to  protect  the  solu- 
tion containing  the  hydrochlorplatinic  acid  from  ammonia. 
Otherwise  there  will  be  formation  of  ammonium  chlorplatinate. 

THE    PERCHLORATE    METHOD    FOR    POTASSIUM 

After  weighing  the  chlorides  of  sodium  and  potassium, 
obtained  as  in  the  preceding  process,  finish  the  separation  as 
follows:  Dissolve  the  mixed  chlorides  in  20  cc.  of  water,  and 


14  QUANTITATIVE  ANALYSIS 

add  sufficient  20  per  cent  solution  of  perchloric  acid  to  convert 
both  sodium  and  potassium  into  the  perchlorates  and  to  have 
a  slight  excess.  Evaporate  to  dryness.  Dissolve  in  10  cc. 
of  water  and  add  a  small  amount  of  perchloric  acid.  Evapo- 
rate again  to  dryness  and  repeat  this  process  until  dense  white 
fumes  of  perchloric  acid  appear.  Allow  to  cool,  and  take  up 
with  25-30  cc.  of  97  per  cent  alcohol,  containing  0.20  per  cent 
perchloric  acid  (i  cc.  of  20  per  cent  solution  to  100  cc.  of  97 
per  cent  alcohol).  Break  up  the  residue  with  a  stirring  rod, 
decant  the  clear  liquid  through  a  Gooch  crucible  containing  an 
asbestos  mat  which  has  been  washed  with  0.20  per  cent  per- 
chloric acid  in  alcohol.  Wash  several  times  by  decantation 
with  alcoholic  perchloric  acid  solution,  transfer  the  residue  to 
the  filter,  and  wash  several  times  on  the  filter.  Dry  the 
crucible  at  120°  for  one  hour,  cool,  and  weigh  as  KC1O4. 

Notes.  —  i.  Potassium  perchlorate  is  insoluble  in  97  per 
cent  alcohol  containing  perchloric  acid,  and  the  sodium  salt 
is  soluble.  This  method  gives  satisfactory  results,  and  has 
the  distinct  advantage  over  the  hydrochlorplatinic  acid 
method  that  it  is  very  much  cheaper. 

The  method  has  been  studied  by  Wense,1  Caspari,2  and 
Baxter 3  and  has  generally  been  accepted  as  accurate,  having 
been  adopted  as  an  official  method 4  by  the  fertilizer  chemists 
of  Germany.  Scholl5  has  applied  the  method  to  the  deter- 
mination of  potassium  in  water  analysis. 

2.  The  method  is  not  accurate  in  the  presence  of  sulphate 
and  ammonium  ions.    The  former  can  be  removed  by  means 
of  barium  chloride  and  the  latter  by  heating. 

3.  The   perchloric  acid  solution  containing  alcohol   should 
never  be  evaporated. 

Dangerous  explosions  may  result.  There  is,  however,  no 
danger  at  the  ordinary  temperature. 

1  Z.  angew.  Chem.,  4,  691  (1891);  5,  233  (1892). 

2  Z.  angew.  Chem.,  6,  68  (1893). 

3  J.  Am.  Chem.  Soc.,  39,  249. 

4  Fifth  Internal.  Congr.  of  Appl.  Chem.,  I,  216  (1903);  4,  940  (1903). 
6  /.  Am.  Chem.  Soc.,  36,  2085. 


ANALYSIS   OF  SPATHIC  IRON  ORE  15 

4.   The  precipitate  is  much  less  soluble  in  alcohol  containing 
a  small  amount  of  perchloric  acid  than  in  alcohol  alone. 


ANALYSIS  OF  SPATHIC  IRON  ORE 
DETERMINATION  OF  SiO2,  MnO,  CaO,  AND  MgO 

Weigh  into  No.  i  lipped  beakers  two  portions  of  the  ore 
of  approximately  0.5  gram  each,  and  dissolve  in  15  cc.  hydro- 
chloric acid  (sp.  gr.  1.12),  heating  to  aid  the  solution.  Filter 
off  the  insoluble  residue,  and  wash  first  with  dilute  hydro- 
chloric acid  and  afterward  with  hot  water.  Ignite  the  paper 
and  residue  at  a  low  temperature,  and  weigh  approximately 
within  5  milligrams.  Cover  with  six  times  the  weight  of 
sodium  carbonate  and  fuse  until  action  ceases.  Add  a  few 
cubic  centimeters  of  water  to  the  crucible  and  warm,  then 
wash  the  contents  of  the  crucible  into  the  original  acid  solu- 
tion. Evaporate  to  dryness  on  the  steam  table,  moisten 
the  dried  mass  with  i  or  2  cc.  of  hydrochloric  acid  (sp.  gr.  1.20), 
and  again  evaporate  to  dryness.  Place  in  a  hot  closet  and 
keep  at  a  temperature  of  no0  C.  for  one-half  hour  to  de- 
hydrate the  silica. 

Moisten  the  residue  with  5  cc.  of  strong  hydrochloric  acid 
and  warm.  Then  add  50  cc.  of  water  and  heat  until  solution 
is  complete.  Filter  immediately,  wash  the  silica  with  dilute 
hydrochloric  acid  (one  part  acid,  sp.  gr.  1.12,  to  three  parts 
of  water)  until  the  filter  shows  no  traces  of  iron,  and  then 
finally  with  hot  water.  Evaporate  the  filtrate  for  the  recov- 
ery of  traces  of  silica,  as  was  done  in  the  silicate  analysis. 
Ignite  both  filters  in  a  platinum  crucible  and  weigh.  Treat 
the  ignited  silica  with  one  or  two  drops  of  water,  enough 
hydrofluoric  acid  to  dissolve  it,  and  two  drops  of  sulphuric 
acid  (i  :  i).  Evaporate  to  dryness  in  a  hydrofluoric  acid 
burner,  ignite,  and  weigh  again.  The  difference  in  weight 
represents  the  silica.  The  weight  of  the  residue  after  the  hy- 
drofluoric acid  treatment  should  not  be  more  than  i  or  2  milli- 
grams at  the  most. 

Concentrate  the  filtrate  from  the  silica,  adding  bromine 


1 6  QUANTITATIVE  ANALYSIS 

water  to  oxidize  the  iron  to  the  ferric  state.  Evaporate 
almost  to  dryness,  or  until  the  ferric  chloride  will  completely 
crystallize  when  allowed  to  cool.  This  operation  must  be 
carried  on  with  caution.  It  is  necessary  to  remove  the  excess 
of  hydrochloric  acid,  but  if  the  evaporation  is  allowed  to  go 
too  far  the  iron  salts  will  become  baked  on  the  bottom  of  the 
vessel,  and  it  will  then  be  necessary  to  dissolve  in  acid  and 
re-evaporate.  When  cold  add  to  the  ferric  chloride  20  cc. 
of  water;  solution  should  be  complete.  If  any  silica  has 
escaped  dehydration  it  will  show  itself  at  this  point,  and  it 
will  be  necessary  to  filter  it  off  and  repeat  the  evaporation  of 
the  filtrate.  Transfer  the  solution  to  a  small  beaker  and  add, 
from  a  burette  or  dropper,  sodium  carbonate  solution  until  a 
precipitate  forms  which  will  dissolve  only  in  two  or  three 
minutes  stirring.  This  point  is  indicated  by  the  solution 
assuming  an  intense  red  color,  and  by  the  ferric  hydroxide 
going  more  and  more  slowly  into  solution.  If  an  excess  of 
sodium  carbonate  should  have  been  added,  it  is  necessary  to 
add  very  dilute  hydrochloric  acid  drop  by  drop,  with  constant 
stirring,  until  the  solution  clears  again ;  then  to  bring  the  solu- 
tion back  to  the  proper  point  with  sodium  carbonate.  Having 
obtained  a  solution  properly  neutralized,  add  10  cc.  of  acetic 
acid  (sp.  gr.  1.04). 

Meanwhile  heat  to  boiling  one  liter  of  distilled  water  for 
each  determination  in  actual  progress,  and  weigh  out  as  many 
portions  of  3  grams  each  of  sodium  acetate.  Transfer  the 
solution  of  the  iron  ore,  together  with  the  liter  of  hot  water, 
to  a  1500  cc.  round-bottom  flask,  and  add  one  portion  of  the 
sodium  acetate  dissolved  in  a  little  hot  water.  Bring  the  so- 
lution to  boiling  and  continue  the  boiling  for  three  minutes. 
If  there  is  any  tendency  to  froth  this  may  be  overcome  by 
pricking  the  bubbles  as  they  form  in  the  neck  of  the  flask 
with  a  long,  glass  stirring  rod.  Remove  the  flask  from  the 
lamp  and  allow  the  precipitate  to  settle.  The  supernatant 
liquid  should  be  colorless  and  clear. 

Filter,  while  still  hot,  through  a  24  cm.  fluted  paper.  Wash 
once  by  decantation  with  250  cc.  of  hot  water.  Dissolve 


ANALYSIS   OF   SPATHIC   IRON  ORE  17 

the  precipitate  in  warm,  dilute  hydrochloric  acid  (sp.  gr. 
1.12),  and  wash  the  filter  paper  until  free  from  iron.  Evapo- 
rate, with  the  addition  of  a  little  bromine  water,  until  a  crust 
forms,  and  repeat  the  basic  acetate  separation  as  described 
above,  this  time  washing  the  whole  of  the  precipitate  onto 
the  filter  paper  and  adding  this  filtrate  to  the  first  one. 

The  combined  filtrates  from  the  two  basic  acetate  separa- 
tions are  evaporated  to  about  400  cc.,  and  bromine  water  is 
added  in  excess.  The  solution  should  be  kept  hot  for  an 
hour,  and  at  the  end  of  this  time  there  still  should  be  a  slight 
odor  of  bromine.  Boil  off  the  excess  of  bromine  and  then 
filter  the  manganese  dioxide,  washing  with  hot  water.  Dis- 
solve any  of  the  precipitate  which  may  have  adhered  to  the 
beaker  in  warm,  dilute  hydrochloric  acid  to  which  a  few  cubic 
centimeters  of  sulphurous  acid  have  been  added.  Pour  this 
solution  through  the  paper  holding  the  manganese  dioxide, 
and  wash  the  paper  with  hot  water  until  entirely  free  from 
chlorides.  Dilute  the  filtrate  to  100  cc.,  add  10  cc.  of  di- 
sodium  phosphate,  10  cc.  of  ammonium  chloride,  and  just 
enough  ammonia  to  produce  a  permanent  precipitate.  Bring 
the  solution  to  boiling,  and  boil  until  the  small  amount  of 
precipitate  appears  to  have  become  crystalline.  Then  add 
ammonia  slowly  until  it  is  present  in  slight  excess,  and  continue 
to  boil,  with  constant  stirring,  until  the  whole  of  the  manga- 
nous  ammonium  phosphate  has  become  silky  and  crystalline. 
Allow  to  stand  until  cold,  filter,  and  wash  with  a  solution  of 
ammonium  nitrate  (10  grams  NHiNO3  in  100  cc.  H2O)  which 
has  been  made  slightly  alkaline  with  ammonia.  Dry  the 
precipitate  and  paper,  place  in  a  platinum  crucible,  and  ignite 
at  as  low  a  temperature  as  possible,  taking  the  same  pre- 
cautions as  is  usual  with  the  corresponding  magnesium 
ammonium  phosphate.  The  paper  should  be  charred  at  as 
low  a  temperature  as  possible,  and  under  no  circumstances 
should  it  be  allowed  to  burn  with  flame.  After  it  is  com- 
pletely charred  the  bottom  part  of  the  inclined  crucible  is 
heated  in  the  oxidizing  flame  of  a  Tirrill  burner  until  the 
precipitate  is  white. 


1 8  QUANTITATIVE   ANALYSIS 

In  the  filtrate  from  the  manganese  dioxide  boil  off  the 
bromine,  evaporate  to  about  400  cc.,  then  add  to  the  boiling 
solution  ammonia  until  slightly  alkaline,  and  ammonium  oxa- 
late  drop  by  drop  until  all  of  the  calcium  has  been  precipi- 
tated, finally  adding  5-10  cc.  in  excess.  Boil  for  several 
minutes,  and  then  allow  to  stand  in  a  warm  place  until  the 
precipitated  calcium  oxalate  has  completely  settled.  Decant 
the  solution  through  a  filter  paper  hi  such  a  way  that  most 
of  the  precipitate  remains  hi  the  beaker.  Add  a  few  cubic 
centimeters  of  ammonium  oxalate  to  the  filtrate  to  see  if 
precipitation  has  been  complete.  Now  dissolve  the  calcium 
oxalate  in  the  beaker  with  hydrochloric  acid,  and  pour  the 
solution  through  the  filter,  receiving  it  in  a  No.  4  beaker 
and  washing  with  hot  water  until  the  washings  amount  to 
250  cc.  Heat  the  solution  to  boiling,  make  slightly  am- 
moniacal,  add  5  cc.  of  ammonium  oxalate,  and  allow  to  stand 
until  the  precipitate  has  completely  settled.  Pour  the  clear 
supernatant  liquid  through  a  filter,  wash  the  precipitate  twice 
by  decantation  with  hot  water,  and  then  transfer  the  whole 
precipitate  to  the  filter  and  wash  until  the  washings  show 
no  test  for  chloride.  Dry  the  precipitate  and  paper,  place 
in  a  platinum  crucible,  and  smoke  off  the  paper  with  a  low 
flame.  After  the  carbon  has  all  been  burned,  heat  the 
covered  crucible  with  the  full  flame  of  a  Tirrill  burner  and 
finally  over  the  blast  lamp  to  constant  weight. 

The  combined  filtrates  from  the  calcium  precipitation  are 
evaporated  to  a  volume  of  400  cc.  If  during  this  evaporation 
there  should  be  a  separation  of  a  white  precipitate  it  will  be 
necessary  to  evaporate  to  dryness  with  concentrated  hydro- 
chloric acid.  If,  however,  there  is  no  precipitation  add 
ammonia  in  excess  and  di-sodium  phosphate,  with  constant 
stirring,  until  precipitation  is  complete.  Allow  to  stand  in 
the  cold  (ice  water)  for  several  hours,  decant  the  solution 
through  a  filter,  and  wash  the  precipitate  onto  the  filter 
with  dilute  ammonia  (three  parts  H2O,  one  part  NE^OH, 
sp.  gr.  0.96),  washing  several  times  with  this  wash  water. 
Now  dissolve  the  precipitate  in  a  small  amount  of  dilute 


ANALYSIS   OF   SPATHIC   IRON   ORE  19 

hydrochloric  acid,  and  wash  the  paper  several  times  with 
water.  To  this  solution  add  5  cc.  di-sodium  phosphate,  and 
then  neutralize  with  ammonia,  adding  it  slowly,  with  stirring, 
until  present  in  very  slight  excess.  After  standing  10  minutes, 
add  10  cc.  strong  ammonia,  sp.  gr.  0.90.  Allow  to  stand 
several  hours  in  ice  water,  filter,  wash  with  dilute  ammonia, 
and  continue  until  a  few  drops  of  the  washing,  acidified  with 
nitric  acid,  shows  no  turbidity  with  silver  nitrate.  Dry  the 
precipitate  and  paper,  and  smoke  off  the  filter  paper  at  as  low 
a  temperature  as  possible,  being  careful  not  to  allow  the  paper 
to  burn  with  flame.  When  charred  raise  the  temperature  of 
heating  to  the  full  flame  of  the  Tirrill  burner  and  continue 
until  the  precipitate  is  perfectly  white. 

DETERMINATION   OF   COMBINED   OXIDES,    Fe203,    A1203,    P2O5 

For  the  determination  of  ferric  oxide,  alumina,  and  phos- 
phoric anhydride  weigh  two  portions  of  approximately  0.2 
gram  each  and  proceed  exactly  as  in  the  determination  of 
manganese,  calcium,  and  magnesium,  except  that  the  silica 
which  is  removed  must  be  treated  with  hydrofluoric  acid,  and 
the  residue  obtained  by  this  operation  must  be  added  to  the 
solution  in  which  iron  and  alumina  are  to  be  determined. 
To  do  this,  fuse  with  a  small  amount  of  sodium  carbonate  and 
dissolve  in  a  small  amount  of  hydrochloric  acid. 

Instead  of  making  a  double  basic  acetate  separation,  as 
was  done  in  the  previous  case,  the  second  precipitation  is 
made  by  means  of  ammonia,  and  the  filtration  is  made  through 
a  closely  fitting  paper.  In  washing,  care  should  be  taken  to 
thoroughly  wash  the  top  of  the  filter.  The  filtrate  from  the 
basic  acetate  separation  should  always  be  evaporated  and 
examined  for  iron. 

Dissolve  the  basic  acetate  precipitate  on  the  filter,  and 
also  any  which  may  have  adhered  to  the  flask,  in  hot,  dilute 
nitric  acid  (sp.  gr.  1.20)  and  wash  the  paper  free  from  iron. 
While  still  warm  add  ammonia  in  slight  excess,  allow  the 
precipitate  to  settle,  decant  through  a  filter  paper,  wash 
twice  by  decantation  with  hot  water,  and  then  transfer  the 


20  QUANTITATIVE   ANALYSIS 

precipitate  to  the  paper  and  wash  several  times  on  the  paper 
with  hot,  dilute  ammonium  nitrate  solution.  Place  the 
washed  and  dried  precipitate  in  a  weighed  platinum  crucible 
and  smoke  off  the  filter  paper  at  a  low  temperature.  This  is 
best  accomplished  by  inclining  the  crucible  on  a  triangle  and 
placing  a  low  flame  under  the  front  end  of  it.  The  flame 
should  be  so  low  that  the  volatile  products  will  smoke  off, 
but  will  not  ignite.  When  the  paper  is  completely  charred, 
ignite  over  the  full  flame  for  fifteen  minutes  and  then  over 
the  blast  lamp  for  five  minutes.  During  this  last  heating  the 
crucible  remains  in  an  inclined  position,  with  the  cover  par- 
tially covering  the  mouth,  but  the  oxidizing  flame  is  directed 
toward  the  bottom  of  the  crucible.  Heat  to  constant  weight. 
The  oxides  thus  obtained  will  always  contain  traces  of 
silica  and  should  be  corrected  for  it.  This  is  done  by  fusing 
the  oxides  with  twelve  times  their  weight  of  acid  potassium 
sulphate  until  the  fusion  becomes  perfectly  clear.  After  the 
fusion  has  become  cold  it  is  dissolved  in  water  and  the  silica 
is  filtered  off,  washed,  ignited,  and  weighed.  This  weight 
subtracted  from  the  weight  obtained  above  gives  the  true 
weight  of  the  combined  oxides. 

DETERMINATION    OF    IRON    IN    SPATHIC    IRON    ORE — 
ZIMMERMANN-REINHARDT  METHOD 

Weigh  three  portions  of  thoroughly  cleaned  iron  wire,  from 
0.15-0.25  gram,  into  150  cc.  Erlenmeyer  flasks,  and  dissolve 
in  20  cc.  of  hydrochloric  acid  (sp.  gr.  1.12)  and  20  cc.  of  water. 
When  the  solution  is  complete,  add  strong  potassium  perman- 
ganate solution  drop  by  drop  until  the  carbonaceous  material 
is  completely  oxidized  and  the  solution  has  shown  a  very 
marked  change  of  color.  Place  the  flasks  on  a  piece  of  white 
paper,  and  reduce  while  still  hot  with  the  smallest  possible 
volume  of  freshly-prepared  stannous  chloride  which  will  pro- 
duce a  colorless  solution.  If  too  much  has  been  added  it  may 
be  corrected  by  adding  potassium  permanganate  solution  until 
a  slight  yellow  coloration  appears,  and  then  adding  just  enough 
stannous  chloride  to  reduce  the  small  amount  of  ferric  chloride 


ANALYSIS  OF  SPATHIC   IRON  ORE  21 

present.  Cool  the  solution  by  holding  the  flask  in  running 
water,  and  when  cold  add  rapidly  10  cc.  of  mercuric  chloride 
(50  grams  per  liter) .  This  should  produce  a  very  small  amount 
of  white,  silky  mercurous  chloride.  If  there  is  a  large  amount 
formed,  or  if  it  is  at  all  dark-colored  or  flocculent,  it  is  not 
advisable  to  try  to  finish  the  titration.  Wash  this  solution 
into  400  cc.  of  cold  water  to  which  has  been  added  20  cc.  of 
manganous  sulphate  solution  (20  grams  MnSO4,  220  cc.  H2O, 
40  cc.  H2SO4  —  sp.  gr.  1.84),  and  titrate  to  pink  color  with 
potassium  permanganate  (3  grams  per  liter)  solution  which 
has  been  filtered  through  asbestos  to  remove  manganese 
dioxide. 

Potassium  permanganate  which  is  to  be  used  in  this  as  well 
as  in  other  determinations  may  be  standardized  accurately 
against  sodium  oxalate  as  follows:  Dissolve  0.25-0.30  gram  of 
sodium  oxalate  in  250  cc.  of  hot  water  in  a  400  cc.  beaker,  and 
add  10  cc.  of  (i  :  i)  sulphuric  acid.  Titrate  with  permanga- 
nate, stir  vigorously,  and  add  the  last  0.5-1.0  cc.  drop  by  drop, 
allowing  each  drop  to  be  decolorized  before  adding  another. 
Estimate  the  excess  of  permanganate  necessary  to  color  the 
solution  by  comparing  with  a  similar  volume  of  water  and 
acid.  The  temperature  of  the  solution  must  be  maintained 
throughout  the  titration  between  70-90°  C. 

To  determine  iron  in  the  spathic  iron  ore  weigh  two  portions 
of  approximately  0.3  gram  each  into  porcelain  crucibles. 
Roast  the  ore  for  ten  minutes  to  destroy  organic  matter, 
and  then  dissolve  in  a  small  quantity,  15-20  cc.,  of  hydrochloric 
acid.  If  there  is  an  insoluble  residue  it  will  be  necessary  to 
fuse  it  with  a  very  small  quantity  of  sodium  carbonate,  take  it 
up  in  hydrochloric  acid,  and  add  it  to  the  main  portion.  When 
the  solution  is  complete,  reduce  with  stannous  chloride,  and 
then  proceed  as  in  the  standardization  of  potassium  perman- 
ganate against  iron  wire. 

Notes.  —  i.  Spathic  iron  ore  is  essentially  ferrous  carbon- 
ate, but  there  is  always  found  with  it  varying  amounts  of 
organic  matter,  silica,  alumina,  manganese,  calcium,  mag- 
nesium, phosphorus,  and  sulphur,  with  traces  of  titanium. 


22  QUANTITATIVE   ANALYSIS 

There  is  invariably  an  insoluble  residue  left  after  treating  with 
hydrochloric  acid,  which  may  contain  some  or  all  of  these 
elements.  After  fusion  of  the  residue  with  sodium  carbonate, 
solution  in  hydrochloric  acid  takes  place  easily. 

A  definite  amount  of  sodium  carbonate  is  prescribed,  so  as 
to  prevent  the  introduction  of  an  unnecessarily  large  excess 
of  sodium  salts,  as  would  probably  be  the  case  if  the  amount 
were  left  to  the  judgment  of  the  worker. 

Four  portions  are  weighed  for  analysis,  because  if  large 
enough  portions  were  taken  to  determine  accurately  the 
manganese,  calcium,  and  magnesium  there  would  be  difficulty 
in  handling  the  very  bulky  precipitate  of  iron  and  alumina; 
consequently  smaller  portions  have  been  taken  for  the  separate 
determination  of  these  constituents. 

2.  The  double  evaporation  of  the  solution  with  hydro- 
chloric acid  is  necessary  in  order  to  dehydrate  completely 
all  of  the  silica.  This  was  shown  to  be  true  by  Hillebrand 
in  the  case  of  silicates,  and  is  even  more  true  here  on  account 
of  the  solvent  effect  of  ferric  chloride.  This  solvent  effect  is 
very  noticeable  if  the  hydrochloric  acid  solution  is  allowed 
to  stand  any  length  of  time  before  filtration. 

It  is  necessary  to  moisten  the  dry  residue  with  hydrochloric 
acid  before  adding  water,  because  of  the  strong  tendency  of 
ferric  and  aluminum  salts  to  hydrolyze  and  form  basic  salts, 
which  would  be  filtered  off  and  weighed  with  the  silica. 
Even  when  the  procedure  is  carefully  followed  there  is  always 
a  slight  residue  left  after  the  hydrofluoric  acid  treatment. 
This  residue  contains  some  iron  and  alumina,  and  traces  of  ti- 
tanium, the  latter  often  being  in  combination  with  phosphoric 
acid. 

The  treatment  with  hydrofluoric  acid  is  based  on  the 
reaction, 

SiO2  +  4HF  =  SiF4  +  2H20, 

but  as  there  is  always  the  tendency  for  the  silicon  tetrafluo- 
ride  to  react  with  water  according  to  this  reaction, 

3SiF4  -f  4H2O  =  2H2SiF6  +  Si(OH)4, 

it  is  necessary  to  have  some  sulphuric  acid  present  to  remove 
the  water  as  fast  as  it  is  formed.  Furthermore,  certain  other 


ANALYSIS   OF  SPATHIC   IRON  ORE  23 

fluorides,  such  as  those  of  iron  and  titanium,  are  volatilized 
in  the  absence  of  sulphuric  acid. 

3.  The  oxidation  of  the  iron  to  the  ferric  state  is  abso- 
lutely   necessary    to    the    success    of    the    operation.      The 
presence  of  ferrous  iron  would  not  only  render  the  separation 
incomplete,  but  it  may  also  cause  the  formation  of  the  so- 
called  "brick-dust"  precipitate,  which  contains  ferrous  iron 
and  is  extremely  difficult  to  handle.     Other  oxidizing  agents 
than  bromine  may  be  used,  but  this  has  been  selected,  not 
only  on  account  of  its  efficiency,  but  also  on  account  of  the 
ease  with  which  the  excess  may  be  removed.     If  nitric  acid 
is  used  as  the  oxidizing  agent  there  sometimes  forms,  on 
evaporation,  a  dark-colored  gummy  mass,  which  can  only  be 
converted  into  the  crystallized  ferric  chloride  by  repeated 
evaporation  with  concentrated  hydrochloric  acid. 

The  careful  evaporation  of  the  excess  of  hydrochloric  acid 
is  to  remove  the  excess  of  oxidizing  agent  and  to  prevent  an 
unnecessary  addition  of  a  large  quantity  of  sodium  carbonate 
when  neutralizing  the  ferric  chloride  solution. 

4.  Ferric  hydroxide  possesses,  to  a  very  high  degree,  the 
property  of  forming  a  colloidal  solution.     When  sodium  car- 
bonate solution  is  added  to  the  ferric  chloride  the  ferric 
hydroxide  which  is  first  formed  gradually  goes  into  solution 
in  the  colloidal  state,  the  increasing  amount  present  being 
indicated  by  the  solution  assuming  the  deep-red  color  charac- 
teristic of  the  undissociated  iron  salts.     As  the  colloidal  con- 
dition is  easily  destroyed  by  heat  and  the  presence  of  an 
electrolyte,  it  is  essential  to  keep  the  solution  cool  until  ready 
for  use,  and  under  no  circumstances  should  the  sodium  acetate 
be  added  to  it  before  dilution. 

The  older  methods  for  the  separation  of  iron  from  man- 
ganese were  based  on  the  decomposition  of  this  colloidal 
solution  by  means  of  heat  in  the  presence  of  an  electrolyte 
(Na2SO4),  which  caused  a  separation  of  the  colloidal  ferric 
hydroxide  and  the  formation  of  a  basic  iron  salt. 

5.  The  separation  of  iron  and  aluminum  from  the  bivalent 
metals  is  based  upon  the  relative  ease  with  which  the  differ- 
ent acetates  hydrolyze.    The  hydrolysis  of  ferric  acetate  may 
be  expressed  in  this  way: 

Fe(CH3C02)3  +  2H20  ^  Fe(OH)2.CH3CO2 


24  QUANTITATIVE   ANALYSIS 

Since  hydrolysis  is  dependent  upon  the  dissociation  of 
water  into  hydroxyl  and  hydrogen  ions,  and  as  the  dissocia- 
tion is  greater  at  the  boiling  temperature,  the  hydrolysis  of 
ferric  and  aluminum  acetates  takes  place  more  rapidly  and 
completely  at  this  temperature.  Manganese  acetate  would 
also  hydrolyze  somewhat  under  the  same  conditions,  espe- 
cially in  neutral  solution,  and  it  is  therefore  necessary  to 
diminish  the  dissociation  of  water  to  such  an  extent  that  the 
ferric  and  aluminum  acetates  may  hydrolyze,  but  that  the 
manganese  acetate  may  not.  This  is  accomplished  by 
the  addition  of  the  wreak  acetic  acid;  and  in  order  that  it, 
and  also  the  acetic  acid  formed  in  the  reaction,  may  not 
furnish  too  great  a  concentration  of  hydrogen  ions,  and  thus 
force  the  water  completely  back  into  the  undissociated  state, 
the  concentration  of  hydrogen  ions  is  diminished  by  the  addi- 
tion of  a  salt  containing  an  ion  in  common,  viz.,  sodium 
acetate.  Consequently  the  strength  of  the  acid  is  weakened. 

If  too  much  acetic  acid  is  used  the  concentration  of  the 
hydroxyl  ion  is  diminished  to  such  an  extent  that  the  ferric 
and  aluminum  acetates  cannot  hydrolyze  completely.  On 
the  other  hand,  if  too  little  acetic  acid  or,  what  is  equivalent 
to  the  same  thing,  too  much  sodium  acetate  has  been  used, 
the  concentration  of  the  hydroxyl  ion  may  be  so  great  that  the 
manganese  acetate  will  also  hydrolyze  and  be  precipitated 
with  the  iron  and  alumina. 

As  the  reaction  involving  the  hydrolysis  is  a  reversible  one, 
it  is  evident  that  in  order  to  force  the  reaction  completely 
in  one  direction  it  is  necessary  to  make  the  nitration  while 
the  solution  is  still  hot.  Otherwise  some  of  the  precipitate 
redissolves  on  cooling. 

6.  If  the  process  has  been  properly  carried  out  the  nitrate 
should  be  clear  and  colorless,  and  free  from  iron.  On  evapo- 
ration any  iron  which  was  not  precipitated  will  separate. 
This,  however,  should  not  be  confused  with  the  hydrated 
manganese  dioxide,  some  of  which  invariably  separates 
during  the  process  of  evaporation,  the  manganous  acetate 
being  oxidized  by  the  air. 

The  best  method  of  deciding  whether  this  precipitate  is 
iron  or  manganese  is  to  filter  it  off,  dissolve  in  a  small 
amount  of  hydrochloric  acid,  and  to  make  a  basic  acetate 


ANALYSIS  OF   SPATHIC   IRON  ORE  25 

separation  in  small  volume.  If  ammonia  and  ammonium 
chloride  are  used  the  separation  may  not  only  be  incomplete, 
but  there  may  be  subsequent  difficulty  in  precipitating  the 
manganese  in  the  main  nitrate  on  account  of  the  presence 
of  ammonium  salts. 

7.  The  basic  acetate  process  is  the  most  accurate  method 
for  the  separation  of  iron  from  manganese.     For  precise  work 
this  method  should  always  be  used,  in  spite  of  some  of  its 
disadvantages.     It  is  also  used  for  the  separation  of  alu- 
minum from  the  bivalent  metals,  but  for  the  separation  of 
chromium  from  the  bivalent  metals  the  barium  carbonate 
process   is   to   be   preferred.     Chromium   acetate   is   incom- 
pletely hydrolyzed  except  in  the  presence  of  a  very  large 
excess  of  iron. 

In  any  case  where  this  separation  is  used  phosphoric  acid 
and  titanium  hydroxide  will  be  precipitated  with  the  trivalent 
elements. 

If  it  is  desired  to  determine  the  iron  in  this  precipitate 
instead  of  making  a  determination  in  a  separate  sample,  it 
may  be  done  by  the  process  described  on  page  20. 

8.  The  double  separation  by  means  of  the  basic  acetate 
process  is  necessary  when  manganese  is  to  be  determined, 
as  there  is  always  some  manganese  carried  down  in  the  first 
precipitation.     This  may  be  partially  due  to  occlusion,  but 
it  is  also  undoubtedly  true  that  in  this  weakly  acid  solution 
some  of  the  manganese  is  oxidized  to  the  dioxide  and  carried 
down  in  this  form. 

9.  When  only  iron  and  aluminum  are  to  be  determined, 
it  is  believed  that  a  single  basic  acetate  precipitation,  followed 
by  a  separation  with  ammonium  hydroxide,  suffices  to  give  a 
pure  precipitate.     The  solution  in  nitric  acid  must  take  place 
before  the  precipitate  has  had  time  to  dry.     If  this  precaution 
is  neglected  it  requires  considerably  more  hot  nitric  acid  to 
dissolve  the  precipitate,  and  in  this  process  the  filter  paper 
is  more  or  less  attacked.    The  solution  will,  therefore,  con- 
tain enough  organic  matter  to  hold  the  iron  and  aluminum  in 
solution  when  ammonia  is  added.    If  the  recently  precipi- 
tated hydroxides  are  dissolved  in  nitric  acid  there  will  be  no 
difficulty  in  making  the  ammonia  precipitation. 

The  use  of  nitric  acid  has  the  distinct  advantage  that  it 


26  QUANTITATIVE   ANALYSIS 

does  away  with  the  tedious  washing  to  remove  chlorides; 
and  furthermore,  it  is  easier  to  keep  the  iron  oxidized  to  its 
highest  state  during  the  ignition. 

Although  some  of  the  aluminum  hydroxide  is  probably 
dissolved  in  the  colloidal  form  when  the  final  washing  is 
made  with  pure  water,  it  is  believed  that  this  may  be  largely 
overcome  by  making  the  final  washing  with  dilute  ammonium 
nitrate  solution. 

10.  Bromine  separates  manganese  dioxide  from  the  ace- 
tate solution  according  to  this  reaction: 


It  would  seem  much  simpler  to  ignite  the  manganese  dioxide 
and  weigh  the  oxide  MrisO^  but  this  process  is  open  to  two 
serious  objections.  In  the  first  place,  manganese  dioxide, 
when  precipitated  from  solutions  containing  sodium  salts, 
occludes  considerable  quantities  of  sodium;  then  the  com- 
position of  the  oxide  formed  on  ignition  is  not  always 
represented  by  the  formula  MngCX  Consequently  it  is 
very  much  more  accurate  to  use  the  excellent  process  de- 
vised by  Gibbs,1  involving  the  separation  of  the  manganese 
as  manganese  ammonium  phosphate,  MnNH4PO4,  and  its  con- 
version by  heat  into  the  pyrophosphate  Mn2P2Oy.  Gooch 
and  Austen2  have  carefully  studied  the  best  conditions  for 
obtaining  a  pure  precipitate.  The  precipitate  which  first 
forms  is  the  tri-manganic  phosphate  Mns(P04)2,  but  this  is 
converted  by  heating  with  an  excess  of  the  precipitant  and 
ammonium  chloride  into  the  crystalline  manganese  ammonium 
phosphate. 

The  same  care  which  is  recommended  in  Note  13  for  the 
ignition  of  magnesium  ammonium  phosphate  should  be  used 
in  this  case.  If  these  precautions  are  neglected  there  will 
be  some  reduction  of  the  precipitate  and  consequent  alloying 
of  the  crucible. 

ii.  The  double  precipitation  of  the  calcium  oxalate  is 
absolutely  necessary  in  order  to  purify  it  from  other  salts 
which  it  carries  down  with  it.  If  there  is  considerable 
aluminum  in  the  ore  it  is  necessary  to  ignite  the  first  calcium 
oxalate  precipitate,  dissolve  the  oxides  in  hydrochloric  acid, 
and  to  add  ammonia  in  very  slight  excess  to  the  solution, 

1  Am.  J.  Sci.  [2],  44,  216.        *  Am.  J.  Set.  [4],  6,  233. 


ANALYSIS   OF   SPATHIC   IRON   ORE  27 

in  order  to  throw  out  traces  of  aluminum  hydroxide,  which 
has  reached  this  point  in  the  analysis  on  account  of  its  having 
been  dissolved  in  the  colloidal  form  when  washing  the  basic 
acetate  precipitate  with  water. 

Richards  1  has  shown  that  magnesium  oxalate  is  carried 
down  with  calcium  oxalate,  and  that  the  amount  of  magnesium 
oxalate  occluded  is  proportional  to  the  amount  of  undis- 
sociated  magnesium  salt  in  solution.  A  double  precipitation  is 
therefore  always,  necessary,  not  only  to  get  a  pure  precipitate  of 
calcium,  but  in  order  to  get  all  of  the  magnesium  into  the 
filtrate. 

It  is  also  well  known  that  sodium  salts  are  occluded  by 
calcium  oxalate. 

12.  The  first  precipitation  of  magnesium  is  made  simply 
with  the  idea  of  removing  it  completely  from  the  rest  of  the 
solution  rather  than  to  get  a  normal  precipitate  of  the  com- 
position represented  by  the  formula  MgNHjPO^     Neubauer z 
has  shown  that  complete  precipitation  takes  place,  even  in 
the  presence  of  a  large  amount  of  ammonium  salts.     He  has 
shown,  and  Gooch  and  Austen  3  have  independently  confirmed 
his  results,  that  a  normal  precipitate  can  only  be  obtained 
in  the  absence  of  ammonium  salts  and  ammonia.     To  ensure 
a  pure  precipitate,  the  solution  must  be  as  nearly  neutral  as 
possible,    as   free   as   possible   from   ammonium   salts,   and 
ammonia  must  be  added  after  the  addition  of  the  phosphate 
solution.     The   large   excess   of  ammonia,   as  prescribed  in 
most   books,   is   distinctly   disadvantageous,   except   in   the 
presence  of  an  excess  of  ammonium  oxalate.     Reidenbach4  has 
shown  it  to  be  necessary  in  this  case.     If,  therefore,  the  first 
precipitation  is  made  in  the  presence  of  an  excess  of  ammonia, 
the  second  precipitation  can  be  made  under  proper  conditions. 

13.  The    ignition    of    magnesium    ammonium    phosphate 
must  be  done  with  extreme  caution.     If  the  initial  heat  is 
applied  too  rapidly  the  ammonia,  which  is  one  of  the  products 
of  the  reaction, 

2MgNH4P04  =  MgzPsOi  +  2NH3  +  H2O, 
is  decomposed,  and  the  hydrogen  then  attacks  the  phosphate, 
reducing  it  and  causing  the  phosphorus  to  alloy  with  the 

1  Richards,  McCaffrey  and  Parker:  Z.  anorg.  Chcm.,  28,  71. 

2  Z.  angew.  Chem.  1896,  435.         3  Am.  J.  Sci.  [3],  7,  187. 
4  Inaug.  Dissertation,  Munich,  1910. 


28  QUANTITATIVE  ANALYSIS 

platinum.  Heraeus,1  who  has  studied  this,  has  shown  that 
this  decomposition  and  reduction  take  place  below  900°  C. 

14.  The  Zimmermann-Reinhardt  method  for  the  determina- 
tion of  iron  has  a  very  distinct  advantage  because  of  the  pos- 
sibility of  using  hydrochloric  acid,  in  which  most  of  the  ores 
are  soluble.     The  reactions  upon  which  the  determination  is 
based  are  as  follows: 

2FeCl3  +  SnCl2      =  2FeCl2  +  SnCU. 

SnCl2  +  2HgCl2  =  SnCl4    +  2HgCl. 
2KMn04  +  ioFeC!2  +  i6HCl  = 

ioFeC!3  -f  2MnCl2  +  2KC1  +  8HO2. 

These  reactions  are  practically  the  same  as  in  the  bichromate 
process  for  the  determination  of  iron,  but  the  use  of  potas- 
sium permanganate  obviates  the  use  of  an  outside  indicator. 

By  using  proper  care,  just  enough  stannous  chloride  can 
be  put  in  to  reduce  the  iron  and  to  have  a  very  slight  excess. 
If  the  operation  is  properly  carried  out,  the  precipitate  of 
mercurous  chloride  is  very  small  in  amount  and  is  silky  in 
appearance.  If  platinum  salts  have  been  introduced  into 
the  analysis,  through  an  acid  potassium  sulphate  fusion,  or 
through  the  solution  in  platinum  of  an  ignited  precipitate, 
it  is  difficult,  and  sometimes  impossible,  to  tell  when  enough 
stannous  chloride  has  been  introduced  into  the  solution. 
When  most  of  the  ferric  iron  has  been  reduced,  then  the 
platinum  begins  to  be  reduced  to  the  platinous  form,  and, 
this  salt  being  highly  colored,  the  solution,  instead  of  be- 
coming colorless,  as  would  ordinarily  be  the  case,  assumes 
the  red  tint  of  the  platinum  salt. 

15.  If  too  small  an  amount  of  hydrochloric  acid  has  been 
used  the  stannic  chloride,  which  is  one  of  the  products  of  the 
reaction,  will  hydrolyze  and  give  products  which  interfere 
with  the  sharpness  of  the  end  point.     If  too  much  hydro- 
chloric acid  is  present  it  will  react  with  the  potassium  per- 
manganate, giving  high  results.     Baxter  and  Frevert 2  have 
shown  that  the  high  results  are  due  to   the  formation  of 
hypochlorous  acid,  which  escapes  from  the  solution  without 
giving  up  its  oxygen,  thus  causing  an  addition  of  a  greater 
amount  of  permanganate  than  would  correspond  to  the  actual 

1  Z.  angew.  Chem.,  15,  917. 

2  Am.  Chem.  J.,  34,  109. 


DETERMINATION  OF   SULPHUR   IN   PYRITE  29 

amount  of  iron  present.  This  reaction  is  completely  cor- 
rected by  the  addition  of  a  manganous  salt,  as  has  been  shown 
by  Kessler  1  and  by  Zimmermann.2  The  mechanism  of  this 
reaction  is  not  completely  understood,  but  the  evidence  points 
toward  the  formation  of  a  manganic  compound,  which  reacts 
with  the  ferrous  iron.  In  other  words,  the  manganese  salt 
catalyzes  the  reaction  between  potassium  permanganate  and 
ferrous  chloride.  On  the  other  hand,  in  a  series  of  interesting 
experiments  on  the  oxidation  of  iron,  some  evidence  has  been 
found  that  iron  is  capable  of  forming  a  peroxide  of  the  formula 
Fe20a,  which  reacts  with  the  ferrous  salt.  This  view,  however, 
would  not  explain  the  fact  that  a  manganese  salt  will  acceler- 
ate the  reaction  between  potassium  permanganate  and  oxalic 
acid,  causing  the  reaction  to  take  place  in  cold  solution,  while 
iron  salts  have  no  effect  upon  this  reaction.3 


DETERMINATION   OF   SULPHUR   IN   PYRITE 

I.  AVAILABLE  SULPHUR  —  LUNGE  METHOD 

Spread  out  on  the  bottom  of  a  200  cc.  casserole  0.4  to 
0.5  gram  of  pyrite  which  has  been  ground  to  extreme  fine- 
ness. Pour  over  this  20  cc.  of  a  freshly  made  mixture  of 
three  volumes  nitric  acid  (sp.  gr.  1.42)  and  one  volume  hydro- 
chloric acid  (sp.  gr.  1.20).  Cover  the  casserole  with  a  watch 
glass  and  warm  gently  until  action  commences;  then  remove 
from  the  heat  until  action  slackens.  Start  the  action  again 
from  time  to  time  and  remove  from  the  heat  when  the  oxides 
of  nitrogen  begin  to  be  evolved.  In  this  way  continue  the 
heating  until  all  action  has  apparently  ceased.  Complete 
disintegration  should  be  accomplished  in  five  to  ten  minutes. 
If  sulphur  separates  it  is  probable  that  the  reaction  was 
allowed  to  proceed  too  violently,  or  that  the  pyrite  was  not 
ground  finely  enough.  In  case  sulphur  has  separated  it  is 
preferable  to  start  with  a  new  sample  rather  than  to  try  to 
oxidize  the  separated  sulphur  by  the  addition  of  potassium 
chlorate. 

1  Z.  anal.  Chem.,  i,  329.  2  Berichte,  14,  779. 

3  For  discussion  and  literature  upon  this  reaction  consult  Barneby,  /.  Am. 
Chem.  Soc.,  36,  1429. 


30  QUANTITATIVE   ANALYSIS 

When  disintegration  is  complete  add  5  cc.  of  sodium  car- 
bonate solution,  and  evaporate  to  dryness  on  the  steam 
bath.  Pour  over  the  dry  mass  5  cc.  of  hydrochloric  acid 
(sp.  gr.  i. 20)  and  again  evaporate  to  dryness.  Moisten  the 
residue  with  i  cc.  of  concentrated  hydrochloric  acid,  warm 
gently  for  a  moment,  then  dilute  with  100  cc.  of  hot  water. 
Filter,  wash  several  times  with  hot  dilute  hydrochloric  acid, 
and  finally  with  hot  water. 

Pour  the  filtrate  into  a  slight  excess  of  ammonia  and  keep 
the  mixture  hot  for  ten  or  fifteen  minutes.  Filter  through 
a  4-inch  Swedish  paper,  wash  first  by  decantation,  and  then, 
throwing  the  precipitate  onto  the  paper,  wash  thoroughly 
with  hot  water. 

If  the  filtrate  and  washings  exceed  250  cc.,  acidify  with 
hydrochloric  acid  and  concentrate  to  approximately  this  vol- 
ume. To  the  boiling,  slightly  acid  solution  add  a  hot  solu- 
tion of  5  per  cent  barium  chloride  from  a  dropper,  allowing 
the  drops  to  run  down  the  inside  of  the  beaker  until  a  slight 
excess  has  been  added.  Allow  to  stand  in  a  warm  place  for 
half  an  hour,  filter,  washing  by  decantation  with  hot  water 
until  the  washings  are  free  from  acid,  and  then  complete  the 
washing  on  the  filter  until  free  from  chlorides. 

When  the  filter  has  drained  as  much  as  possible  from 
wash  water,  fold  it  over  the  barium  sulphate,  and  place  it 
in  the  bottom  of  a  weighed  platinum  crucible.  Incline  the 
crucible  on  its  side,  with  the  lid  partially  covering  the  front, 
and  place  under  the  front  end  a  flame  so  small  that  it  will 
dry  the  paper  so  slowly  that  there  is  no  danger  of  spatter- 
ing, and  that  it  will  char  the  paper  without  having  it  take  fire. 
When  the  paper  is  completely  charred,  place  under  the  back 
of  the  crucible  the  full  oxidizing  flame  of  a  Tirrill  burner, 
and  heat  thirty  minutes.  As  some  of  the  barium  sulphate 
is  invariably  reduced  to  sulphide,  it  is  necessary  to  allow  free 
access  of  air  into  the  crucible,  and  to  continue  the  heating 
until  constant  weight  is  obtained. 


DETERMINATION  OF  SULPHUR  IN  PYRITE  31 

H.    AVAILABLE   SULPHUR  —  METHOD   OF  ALLEN  AND 
BISHOP1 

About  0.5  gram  of  the  dried  ore  is  put  in  a  dry  300  cc. 
Pyrex  beaker,  10  cc.  of  a  mixture  of  2  parts  by  volume  liquid 
bromine  and  3  parts  carbon  tetrachloride  are  added  and 
the  beaker  is  covered  with  a  watch  glass.  After  standing 
15  minutes  at  room  temperature  with  occasional  gentle 
shaking,  10  cc.  nitric  acid  (sp.  gr.  1.4)  are  added  and  the 
mixture  is  allowed  to  stand  fifteen  minutes  longer  at  room 
temperature  with  occasional  shaking.  The  beaker  is  then 
placed  on  an  asbestos  board  on  top  of  the  steam  bath  and 
allowed  to  remain  there  until  all  action  has  ceased  and  most 
of  the  bromine  has  been  volatilized.  It  is  then  placed  within 
the  rings  of  the  bath  and  the  solution  evaporated  to  dryness, 
the  cover  glass  being  raised  above  the  rim  of  the  beaker  by 
means  of  riders  made  of  bent  glass  rods.  Ten  cc.  hydro- 
chloric acid  (sp.  gr.  1.2)  are  next  added,  and,  after  shaking 
to  mix  thoroughly,  the  solution  is  evaporated  to  dryness, 
still  keeping  the  beaker  covered  as  in  the  former  evaporation. 
When  completely  dry  the  silica  is  dehydrated  by  heating  in 
an  air  bath  at  100°  C.  for  several  hours. 

One  cc.  of  hydrochloric  acid  (sp.  gr.  1.2)  are  now  added  to 
the  dehydrated  mass,  followed  after  five  minutes  by  50  cc. 
of  hot  water.  The  cover,  sides  of  beaker,  and  riders  are  care- 
fully washed  down  with  hot  water  and  after  the  removal  of  the 
riders  the  cover  is  replaced.  The  mixture  is  heated  for  five 
minutes  to  insure  complete  solution  of  all  sulphate.  After 
the  solution  has  partially  cooled  by  standing  for  about  five 
minutes,  o.i  gram  of  powdered  aluminum  is  added  and 
the  beaker  gently  stirred  until  the  iron  color  has  disappeared, 
showing  complete  reduction.  It  is  now  advisable  to  cool 
the  solution  to  prevent  possible  mechanical  loss  of  material 
in  the  form  of  mist  when  filtering,  due  to  the  action  of  warm 
hydrochloric  acid  on  the  excess  of  aluminum  powder.  After 
cooling,  the  cover  glass  and  sides  of  the  beaker  are  washed 

1  Eighth  International  Congress  of  Applied  Chemistry,  I,  33;    /.  Ind.  Eng. 
Chem.,8, 1167;  /.  Ind.  Eng.  Chem.,  11, 45- 


32  QUANTITATIVE  ANALYSIS 

down  and  the  solution  is  filtered  through  an  n  cm.  filter  paper 
into  a  No.  7  beaker  and  the  residue  washed  thoroughly  with 
hot  water.  To  the  filtrate  are  added  3  cc.  more  of  hydrochloric 
acid  (sp.  gr.  1.2)  and  sufficient  cold  water  to  dilute  to  650  cc. 
After  stirring  to  mix  well,  the  beaker  is  covered  with  a  large 
cover  glass  and  the  sulphate  precipitated  by  adding  through 
a  special  form  of  " precipitating  cup"  (discharging  at  the  rate 
of  5  cc.  per  minute)  50  cc.  of  5  per  cent  barium  chloride  solu- 
tion. The  solution  is  not  stirred  while  the  barium  chloride 
is  being  added  but  after  all  is  in,  the  supernatant  liquor  is 
mixed  by  gentle  stirring. 

After  the  barium  sulphate  has  settled  it  is  filtered  through 
a  tared  Gooch  crucible,  using  suction.  The  Gooch  crucible 
used  has  a  capacity  of  35  cc.,  with  perforated  bottom  attached, 
and  with  a  moderately  thick  asbestos  mat.  The  clear  liquid 
is  siphoned  through  the  crucible,  the  precipitate  is  transferred 
to  the  filter  by  a  stream  from  a  wash  bottle,  and  the  beaker 
washed  six  times  with  cold  water.  The  crucible  is  then 
ignited  slowly,  placing  it  first  on  an  asbestos  board  over  a 
flame  for  25  minutes  so  as  to  expel  the  water  gradually,  or  it 
may  be  given  this  preliminary  drying  by  placing  it  in  the  steam 
oven  for  a  few  hours  if  more  convenient.  The  crucible  is 
placed  upon  the  lid  of  a  platinum  crucible  and  is  then  heated 
with  the  full  flame  of  a  Tirrill  burner  for  thirty  minutes,  cooled 
in  a  desiccator,  and  weighed. 

III.    TOTAL   SULPHUR  —  FRESENIUS   METHOD 

Mix  0.4  to  0.5  gram  finely  ground  pyrite  with  ten  parts  of  a 
mixture  of  four  parts  sodium  carbonate  and  one  part  potassium 
nitrate  in  a  platinum  crucible. 

Cut  an  opening  in  an  asbestos  board  (at  least  4  inches 
square)  sufficiently  large  to  allow  the  lower  two-thirds  of  the 
crucible  to  project  below  the  board.  Place  the  covered  cru- 
cible in  this  opening,  heat  gently  at  first,  and  finally  raise 
the  temperature  enough  to  bring  the  mass  to  fusion.  Any 
unnecessary  increase  in  the  heat  should  be  avoided  on  account 
of  the  action  of  the  oxidizing  mixture  on  the  platinum.  Keep 


DETERMINATION  OF  SULPHUR   IN   PYRITE  33 

the  mass  in  fusion  fifteen  minutes,  stirring,  if  necessary,  with 
a  stout  platinum  wire  to  prevent  the  fusion  from  caking  on  the 
sides  of  the  crucible. 

When  the  action  has  apparently  ceased,  place  the  crucible 
in  a  porcelain  casserole,  and  extract  the  residue  several  times 
with  boiling  water.  Decant  the  solution  through  a  filter 
paper  and  then  boil  the  residue  with  20  cc.  of  a  10  per  cent 
solution  of  sodium  carbonate.  Finally,  wash  the  residue 
thoroughly  with  a  i  per  cent  solution  of  sodium  carbonate. 

Make  the  filtrate  distinctly  acid  and  add  5  cc.  of  hydro- 
chloric acid  (sp.  gr.  1.20)  in  excess.  Boil  to  expel  the  carbon 
dioxide  and  evaporate  to  dryness.  Moisten  the  residue  with 
5  cc.  concentrated  hydrochloric  acid  and  again  evaporate  to 
dryness.  Then  warm  the  residue  gently  with  2  cc.  of  hydro- 
chloric acid  (sp.  gr.  1.20)  and  add  100  cc.  of  hot  water;  filter, 
and  wash  the  silica. 

In  the  filtrate,  which  should  amount  to  about  250  cc., 
the  sulphuric  acid  is  precipitated  in  boiling  solution  by  hot 
barium  chloride,  as  in  the  Lunge  method,  and  the  barium 
sulphate  should  be  filtered,  washed,  and  ignited  in  the  same 


IV.    TOTAL   SULPHUR  —  SODIUM  PEROXIDE   METHOD  : 

Mix  thoroughly  about  0.5  gram  of  finely  ground  pyrite  with 
5  grams  sodium  peroxide  and  4  grams  sodium  carbonate  in  an 
iron  crucible.  Place  the  crucible  in  an  opening  cut  in  an 
asbestos  board,  heat  gently  for  ten  minutes  and  then  raise 
to  the  full  heat  of  a  Tirrill  burner  for  25  minutes.  Allow  the 
crucible  to  cool,  place  in  a  casserole  containing  150  cc.  of  water, 
digest  until  the  sodium  salts  are  dissolved.  Remove  the 
crucible,  wash  with  hot  water,  and  to  the  solution  add  5  cc. 
of  hydrochloric  acid  (sp.  gr.  1.20)  which  has  been  saturated 
with  bromine.  Heat  to  boiling,  filter  the  ferric  hydroxide, 
and  wash  free  from  sulphate.  Acidify  the  filtrate  with  hydro- 
chloric acid,  evaporate  to  dryness  to  remove  silica,  take  up  in 

1  Hempel,  Z.  anorg.  Chem.,  3,  193;  Clark,  /.  Chem.  Soc.,  63,  1079;  Glaser, 
Chem.  Zlg.,  18,  1448. 


34  QUANTITATIVE  ANALYSIS 

2  cc.  of  hydrochloric  acid  (sp.  gr.  1.20)  and  add  100  cc.  of  hot 
water;  filter  and  wash. 

In  the  filtrate,  precipitate  the  sulphate  and  proceed  exactly 
as  in  the  Lunge  method. 

Notes.  —  i.  The  very  great  commercial  importance  of 
pyrite  makes  the  accurate  estimation  of  sulphur  one  of  the 
most  important  determinations  in  the  whole  field  of  analyt- 
ical chemistry.  For  the  determination  of  available  and  total 
sulphur,  the  methods  of  Lunge  and  Fresenius,  respectively, 
are  undoubtedly  the  most  accurate.  The  Lunge  method 
determines  only  that  portion  of  the  total  sulphur  which  is 
available  for  the  manufacture  of  sulphuric  acid;  the  Frese- 
nius method  determines  all  of  the  sulphur  irrespective  of  the 
form  in  which  it  exists.  Very  many  other  methods  have 
been  proposed,  but  none  of  them  has  met  with  such  general 
favor  as  these  two,  and  they  can  at  this  time  be  considered 
as  standards  for  this  determination. 

2.  The  Fresenius  method  has  the  disadvantage  that  the 
oxidizing  flux  attacks  the  platinum  crucible  badly  and,  further- 
more, it  is  always  necessary  to  completely  destroy  the  nitrate 
before  precipitating  the  sulphate  ion.     It  has  been  repeatedly 
demonstrated  that  the  sodium  peroxide  method  gives  entirely 
satisfactory  results,  and  it  has  the  advantage  of  being  more 
rapid  than  the  Fresenius  method.    Occasionally  the  water 
extract  of  the  fusion  shows  the  presence  of  manganate  or  per- 
manganate and  this  may  be  destroyed  by  the  addition  of  a  few 
drops  of  alcohol. 

3.  If  the  reaction  in  the  Lunge  method  is  allowed  to 
begin  too  vigorously  there  is  invariably  a  separation  of  sul- 
phur, and,  while  it  is  possible  to  oxidize  the  separated  sulphur, 
it  is  only  done  at  the  expense  of  much  time  and  after  the 
addition  of  considerable  potassium  chlorate. 

The  Lunge  method  cannot  be  used  for  the  decomposition 
of  many  of  the  native  sulphides  on  account  of  the  strong 
tendency  of  some  of  them  to  liberate  their  sulphur  in  the 
free  state.  By  using  pure  fuming  nitric  acid,  or  by  reversing 
the  proportions  of  nitric  and  hydrochloric  acids,  the  decom- 
position and  oxidation  of  most  sulphides  may  be  accomplished 
successfully. 


DETERMINATION  OF   SULPHUR  IN  PYRITE  35 

The  Allen  and  Bishop  method  has  the  advantage  over  the 
Lunge  method  in  that  it  efficiently  takes  care  of  separated 
sulphur.  The  carbon  tetrachloride  dissolves  the  sulphur 
immediately  on  its  separation  and  it  is  then  oxidized  by  the 
bromine  also  held  in  solution  by  this  solvent. 

4.  It   is   necessary   in   all   cases,   before  precipitation   of 
barium  sulphate,  to  remove  completely  all  traces  of  nitric  or 
nitrous  acids  by  repeated  evaporation  with  hydrochloric  acid. 
It  was  shown  as  early  as  1842  by  Mitscherlich  that  barium 
sulphate  carried  down  many  salts  from  solution;  on  the  other 
hand,  its  complete  precipitation  is  inhibited  by  the  presence 
of  certain  salts.    In  either  case,  when  an  accurate  determi- 
nation of  sulphur  is  to  be  made,  the  salts  which  interfere 
with  the  precipitation  must  be  removed  before  barium  chlo- 
ride is  added  to  the  solution.    Among  the  more  common 
substances  which  are  carried  down  with  barium  sulphate  are 
the  chloride,  nitrate,  and  chlorate  of  barium,  sodium,  and 
potassium;   copper,  zinc,  iron,  and  aluminum  salts.     Some 
interesting   experiments   have   been   made   by   Hulett   and 
Duschak,1  showing  the  amounts  of  barium  chloride  actually 
carried  down  with  the  barium  sulphate.     They  have  also 
devised  a  very  simple  method  by  which  corrections  can  be 
made  for  this  error.     The  complete  precipitation  of  all  of 
the  sulphuric  acid  in  solution  is  interfered  with  by  the  pres- 
ence of  chromium  salts,  metaphosphoric  acid,  etc. 

5.  The  precipitation  of  barium  sulphate  in  the  presence 
of  ferric  iron  has  received  attention  from  a  large  number  of 
investigators.     It  has  been  known  for  a  long  time  that  low 
results  are  obtained  when  barium  sulphate  is  precipitated 
from   solutions   containing  ferric  iron,   notwithstanding  the 
fact  that  the  precipitate  is  contaminated  with  ferric  oxide. 
In  the  process  of  ignition  sulphur  trioxide  is  lost,  and  the 
amount  lost  more  than  counterbalances  the  weight  of  the 
ferric  oxide.    The  old  method  of  fusing  the  ignited  precipi- 
tate with  an  alkaline  carbonate  if  it  showed  a  red  color,  led  to 
inaccurate  results,  although  insuring  a  purer  precipitate.  Some 
of  the  sulphuric  acid  was  always  lost  during  the  process  of 
ignition,  the  amount  depending  upon  the  tune  and  temperature 
of  heating. 

Various  remedies  have  been  proposed  hi  order  to  overcome 
1  Z.  anorg.  Chem.,  40,  196. 


36  QUANTITATIVE   ANALYSIS 

the  difficulty  of  the  precipitation  of  barium  sulphate  in  the 
presence  of  iron  salts.  These  remedies  may  be  classed  under 
three  heads: 

(1)  Removal  of  the  iron  before  precipitation. 

(2)  Conversion  of  the  ferric  ion  into  a  complex  ion. 

(3)  Conversion  of  the  ferric  ion  to  the  ferrous  ion. 

The  Fresenius  method  is  the  best  representative  of  the 
first  principle.  In  this  case  the  iron  is  completely  removed 
as  the  oxide,  and,  after  the  subsequent  removal  of  nitrous 
and  nitric  acids  by  evaporation  with  hydrochloric  acid,  the 
precipitation  may  be  carried  out  under  the  most  favorable 
conditions. 

In  the  Lunge  method  this  same  result  is  reached  by  pre- 
cipitation of  the  iron  by  means  of  ammonia.  Many  chemists 
have  claimed  that  this  precipitation  of  ferric  hydroxide  always 
gave  inaccurate  results  on  account  of  the  retention  of  basic 
iron  sulphate  in  the  ferric  hydroxide  precipitate.  Lunge  has 
repeatedly  expressed  the  firm  conviction,  however,  that  if 
the  method  is  carried  out  as  he  directs  there  will  be  no  loss 
on  this  account.  Gladding  l  modified  the  method  so  as  to 
obviate  the  tedious  washing  of  the  ferric  hydroxide  precipi- 
tate. He  recommended  redissolving  the  ferric  hydroxide  in 
hydrochloric  acid  and  then  adding  barium  chloride  to  this 
solution  to  recover  the  small  amount  of  sulphuric  acid  carried 
down. 

The  most  interesting  modification  of  the  Lunge  method 
involving  the  same  principle  is  that  of  Kiister  and  Thiel.2 
They  advised  the  precipitation  of  the  ferric  ion  by  an  excess 
of  ammonia  and  the  addition  of  barium  chloride  to  this  solu- 
tion, dissolving  the  ferric  hydroxide  after  the  complete  pre- 
cipitation of  the  barium  sulphate.  This  method  overcomes 
the  objection  raised  by  Gladding,  in  that  it  removes  the  iron 
from  solution,  and  furthermore  it  does  away  with  a  trouble- 
some filtration.  The  results  obtained  by  this  method  are  un- 
doubtedly higher  than  those  obtained  by  the  Lunge  method. 
Whether  or  not  this  is  due  to  a  certain  counterbalancing  of 
errors  remains  to  be  seen  after  further  experiments  have 

1  /.  Amer.  Chem.  Soc.,  16,  401. 

2  Z.  anorg.  Chem.,  19,  98. 


DETERMINATION  OF   SULPHUR  IN  PYRITE  37 

been  tried.  It  is  highly  probable  that  the  occlusion  of  barium 
chloride  by  the  precipitation  of  the  barium  sulphate  in  the 
ammoniacal  solution  would  be  considerable.  Lunge l  has 
admitted  and  shown  by  a  series  of  experiments  that  his  own 
method  gives  accurate  results  only  because  of  a  counter- 
balancing of  errors. 

The  conversion  of  the  ferric  ion  into  a  complex  ion  was 
first  suggested  by  Jannasch  and  Richards,2  who  used  for  this 
purpose  formic,  acetic,  and  citric  acids,  and  this  was  extended 
by  Kiister  and  Thiel,3  who  used  oxalic  and  tartaric  acids; 
but  in  neither  case  were  the  results  entirely  satisfactory,  as 
the  precipitates  were  invariably  colored  by  occluded  iron. 

The  conversion  of  the  ferric  into  the  ferrous  ion  also 
originated  with  Jannasch  and  Richards,4  but  the  results  by 
this  method  have  not  been  entirely  satisfactory.  When 
zinc  and  hydrochloric  acid  are  used  for  the  reduction,  the 
zinc  in  solution  is  always  carried  down  by  the  barium  sul- 
phate. In  the  hands  of  some  chemists  this  method  has  been 
more  satisfactory,  although  it  has  not  come  into  general  use. 

No  completely  satisfactory  explanation  has  yet  been  offered 
as  to  why  barium  sulphate  carries  down  iron  salts  nor  why 
solutions  containing  iron  salts  will  retain  some  barium  sul- 
phate. Some  evidence  has  been  offered  by  Jannasch  and 
Richards 5  for  the  existence  of  a  barium  ferric  sulphate, 
and  this  idea  has  been  subjected  to  experimental  study  by 
Schneider,6  who  came  to  the  conclusion  that  a  solid  solu- 
tion of  low  concentration  was  formed.  On  the  other  hand, 
Ostwald  7  has  called  attention  to  the  analogy  with  chromium 
salts,  which  on  heating  form  a  complex  ion  containing  the 
SOi  group,  which  does  not  react  with  barium  ions.  Kiister 
and  Thiel 8  developed  this  idea  and  assumed  that  some  such 
complex  as  Ba[Fe(SO4)2]2  is  formed,  but  they  admit  from 
the  data  at  hand  that  it  is  impossible  to  say  what  the 
nature  of  the  complex  is.  It  seems  probable  that  the  true 
explanation  will  be  that  barium  sulphate  is  capable  of  form- 
ing a  solid  solution  with  some  product  of  the  hydrolysis  of 
ferric  sulphate. 

1  Z.  angew.  Cltem.,  1904,  913;  1905,  1921.  2  /.  prak.  Chem.,  147,  325. 

3  Z.  anorg.  'Chem.,  19,  97.  *  J-  prak.  Chem.,  147,  322. 

6  /.  prak.  Chem.,  147,  332.  •  Z.  phys.  Chem.,  10,  425. 

7  Z.  phys.  Chem.,  29,  340.  8  Z.  anorg.  Chem.,  25,  322. 


49108 


38  QUANTITATIVE  ANALYSIS 

Smith1  reaches  the  conclusion  that  barium  sulphate  precipi- 
tates thrown  down  in  presence  of  ferric  iron  carry  with  them 
a  hydrated  complex  sulphato-ferriate  of  barium  or  other  cation 
which  is  present  in  intimate  mechanical  mixture  with  the 
barium  sulphate. 

6.  The  explanation  of  the  occlusion  of  barium  chloride 
is  very  much  more  satisfactory.  Hulett  and  Duschak  have 
carefully  determined  the  amounts  of  barium  chloride  carried 
down  by  barium  sulphate  under  varying  conditions,  and  have 
offered  an  explanation  of  this  occlusion  which  seems  to  be 
satisfactory.  They  have  found  that  barium  sulphate  carefully 
washed  and  dried  at  140°  contains  not  only  barium  chloride, 
but  also  chlorine  in  some  form  of  combination  which  splits 
off  hydrochloric  acid  at  higher  temperatures.  Reasoning  by 
analogy,  they  assume  that  barium  chloride  may,  like  lead  and 
mercuric  chlorides,  dissociate  not  directly  into  Ba  and  Cl 
ions,  but  the  dissociation  may  take  place  in  this  way: 


Bad'  *±  Ba"     +  Cl'. 

In  like  manner  sulphuric  acid  also  dissociates: 
H2SO4<^HS04'  +H* 
HS04±+S04"     +H\ 

On  the  assumption  of  such  partial  dissociation,  Bad*  ions 
could  combine  with  HSO'4  ions  to  form  the  salt  BaCl'HS04, 
which,  upon  being  sufficiently  heated,  would  split  off  hydro- 
chloric acid  and  leave  neutral  BaSO4.  Hulett  and  Duschak 
also  assumed  the  possibility  of  such  reactions  as  the  following 
taking  place: 

I.    .BaCT+SCV'^SO,.  -' 


•II. 

TTQ/"V 

When  the  salt        _   /  Ba  is  heated  it  should  give  off  sul- 
HSO4  * 

phuric  acid  and  leave  barium  sulphate;  when  heated  together 

with  more  than  the  equivalent  of  SO4,  hydrochloric 

Bad  S 

acid  should  form;  and  when  heated  with  less  than  the  equiv- 

alent, then  we  should  expect  both  hydrochloric  and  sulphuric 

1  /.  Amer.  Cltem.  .b'oc.,  39,  1152. 


DETERMINATION  OF  TITANIUM  IN  TITANIUM  IRON  ORE      39 

acids.  This  condition  was  actually  realized  by  Folin,1  who 
studied  the  conditions  under  which  either  one  or  the  other 
of  these  two  salts  should  form.  He  also  suggested  the  possi- 
bility of  formation  of  salts  of  the  character  represented  by 

the  formula  ..-.,.,_    x  Ba  in  which  M  represents  any  metal. 
M  o(J4/ 

This  would  account  for  the  carrying  down  of  potassium  when 
barium  sulphate  is  precipitated  in  its  presence. 

7.  Too  long  and  too  high  heating  of  the  fusion  in  the 
Fresenius  method  will  cause  considerable  attack  upon  the 
platinum  crucible,  and  consequently  the  introduction  of  plati- 
num into  the  analysis.  If  other  constituents  than  sulphur  are 
to  be  determined,  this  fact  must  be  taken  into  consideration, 
and  the  platinum  removed  accordingly. 

The  completeness  of  the  reaction  may  be  judged  by  the 
appearance  of  the  residue  after  fusion.  It  should  have 
the  color  of  rouge.  If  black,  it  will  contain  ferrous  sulphide. 

The  use  of  coal  gas  for  heating  the  crucible  is  almost 
unavoidable  in  a  large  laboratory,  but  in  small  laboratories 
the  use  of  an  alcohol  lamp  is  strongly  advised.  The  deflec- 
tion of  the  products  of  combustion  by  means  of  an  asbestos 
board  partially  overcomes  the  difficulty. 

That  barium  sulphate  is  easily  reduced  to  sulphide  during 
the  process  of  ignition  is  not  sufficiently  recognized.  As 
much  care  should  be  used  in  the  ignition  of  this  precipitate 
as  in  the  ignition  of  magnesium  ammonium  phosphate. 

It  should  also  be  remembered  that  under  no  circumstances 
is  it  permissible  to  heat  barium  sulphate  over  the  blast  lamp. 
Above  900°  it  loses  sulphur  trioxide,  and  the  residue  becomes 
alkaline,  owing  to  loss  of  sulphur  trioxide. 

DETERMINATION    OF    TITANIUM    IN    TITANIUM 
IRON    ORE 

I.    METHOD   OF   GOOCH 2 

Fuse  0.4-0.6  gram  of  finely-ground  ore  with  6  to  8  times 
its  weight  of  sodium  carbonate  until  action  ceases.  Extract 
the  mass  with  hot  water,  and  decant  the  solution  through  a 

1  J.  Biol.  Chem.,  I,  131. 

2  Chemical  News,  52,  55,  68. 


40  QUANTITATIVE  ANALYSIS 

filter.  Boil  the  residue  with  25  cc.  of  sodium  carbonate  solu- 
tion, filter,  and  then  wash  the  residue  on  the  filter  paper 
several  times  with  dilute  sodium  carbonate  solution.  Place 
the  filter  and  residue  in  a  platinum  crucible,  and  ignite  at  a  low 
temperature  until  the  filter  paper  is  burned.  Fuse  with  12  to 
15  parts  of  dry  potassium  pyrosulphate  for  one-half  hour. 
The  temperature  of  the  fusion  should  be  so  regulated  that  the 
mass  is  kept  in  the  molten  condition,  but  sulphur  trioxide 
should  escape  only  when  the  lid  of  the  crucible  is  removed. 
Cool,  and  remove  the  fusion  from  the  crucible  by  means  of  a 
platinum  wire.  Suspend  the  fusion  in  200  cc.  of  cold  water, 
to  which  has  been  added  100  cc.  of  sulphurous  acid,  and  allow 
to  stand  in  a  cool  place  until  solution  is  complete. 

Filter  if  necessary.  To  the  solution  add  125  cc.  of  acetic 
acid  (sp.  gr.  1.04),  and  dilute  to  800  cc.  in  a  liter  beaker.  Add 
20  grams  of  ammonium  acetate  dissolved  in  a  small  amount  of 
water  and  boil  from  3  to  5  minutes,  adding,  just  before  the 
boiling  point  is  reached,  an  additional  25  cc.  of  sulphurous 
acid.  Allow  to  stand  in  a  warm  place  for  one-half  hour  and 
then  filter,  by  means  of  a  siphon,  through  a  9  cm.  paper. 

Wash  the  precipitate  with  five  per  cent  acetic  acid  solution 
until  most  of  the  sulphate  has  been  removed,  and  then  ignite 
the  paper  and  precipitate  at  a  low  temperature.  Fuse  with 
potassium  pyrosulphate  again.  Proceed  exactly  as  before, 
finally  igniting  to  constant  weight  and  weighing  the  precipitate 
asTiOa. 

Notes.  —  i.  Titanium  iron  ore  is  essentially  ferrous  titanate 
of  the  composition  represented  by  the  formula  FeTiO3,  but  it 
rarely  occurs  in  this  form  except  in  isolated  crystals.  In  the 
massive  form  it  approximates  this  composition,  but  it  is 
always  contaminated  with  silica,  phosphorus,  alumina,  man- 
ganese, calcium  and  magnesium.  It  is  of  small  importance 
at  the  present  time  as  an  iron  ore,  but  it  is  the  source  from 
which  ferro-titanium,  an  increasingly  useful  product,  is 
obtained. 

2.  As  some  of  the  titanium  ores  are  very  refractory  and  do 
not  yield  to  treatment  with  acids,  special  methods  have  been 


DETERMINATION  OF  TITANIUM  IN  TITANIUM  IRON  ORE      41 

devised,  not  only  for  getting  the  ores  into  solution,  but  also 
for  some  of  the  separations  necessary.  Even  if  the  ore  proved 
to  be  acid  soluble,  silica  cannot  be  removed  by  the  usual 
process  of  evaporation  to  dryness,  on  account  of  the  formation 
of  insoluble  compounds  containing  phosphorus  and  titanium. 
It  is,  therefore,  customary  to  remove  silica  and  phosphorus 
together  by  fusing  the  ore  with  sodium  carbonate.  The 
silicate  and  phosphate  of  sodium  are  leached  out  and  removed 
from  the  insoluble  sodium  titanate,  ferric  oxide,  and  carbon- 
ates of  the  alkaline  earths.  Some  of  the  aluminum  goes  into 
the  nitrate,  and  part  remains  in  the  residue. 

3.  Ignition  of  the  sodium  titanate  residue  must  be  made 
at  a  low  temperature,  as  it  becomes  less  soluble  on  prolonged 
or  high  heating. 

4.  Fusion  of  any  substance  with  potassium  pyrosulphate 
requires  considerable  skill,  patience  and  caution.     The  pre- 
liminary heating  should  be  carried  out  slowly  and  at  a  low 
temperature,  on  account  of  the  tendency  to  froth  over,  which 
always  results  in  the  loss  of  the  determination,  and  sometimes 
in  serious  burns.    To  avoid  as  far  as  possible  the  frothing, 
which  is  most  vigorous  during  the  first  part  of  the  heating, 
potassium  pyrosulphate  should  be  used,  and  not  the  acid 
potassium  sulphate.    The  former  may  easily  be  made  by 
heating  the  latter  to  fusion  for  a  very  short  time.     Prolonged 
heating  leads  to  the  formation  of  the  normal  sulphate  which 
expands  on  solidification  and  may  crack  the  crucible. 

It  is  an  inexcusable  mistake  to  try  to  hurry  the  solution  of 
the  sulphate  fusion  by  heating.  Hydrolysis  invariably  takes 
place,  with  the  formation  of  a  colloidal  solution. 

5.  The  separation  of  titanium  from  iron,  aluminum  and 
manganese  is  based  upon  the  same  principle  involved  in  the 
separation  of  iron  and  aluminum  from  manganese,  as  given 
under  the  Analysis  of  Spathic  Iron  Ore.1    The  iron  is  pre- 
vented from  hydrolyzing  by  being  kept  in  the  ferrous  condi- 
tion, and  the  aluminum  and  manganese  are  prevented  by 
having  a  hydrogen  ion  concentration  so  great  that  they  will 
not  hydrolyze,  but  titanium  may  hydrolyze  completely,  and 
precipitate. 

Titanium  will  hydrolyze  completely  on  continued  boiling 
from  strong  acid  solutions,  but  it  usually  separates  in  such  a 
1  Page  23,  note  5. 


42  QUANTITATIVE   ANALYSIS 

form  as  to  make  its  filtration  difficult,  if  not  impossible.  If 
the  directions  are  carefully  followed,  titanium  hydroxide 
should  separate  quickly  and  in  a  flocculent  form  which  filters 
with  comparative  rapidity. 

6.  Separation  of  iron  and  titanium  by  this  method  is  usually 
complete,  although  a  second  precipitation  is  necessary.    Other 
methods  for  the  separation  of  these  two  elements  have  been 
recommended,  the  most  promising  of  which  depends  upon  the 
solubility  of  ferric  chloride  in  ether. 

7.  Colorimetric  estimation  of  titanium,1  when  present  in 
small  amounts,  is  not  only  rapid,  but  very  accurate.     The 
method  is  based  upon  the  reaction  which  takes  place  between 
titanium  salts  and  hydrogen  peroxide.    The  intense  yellow 
color  produced  is  compared  with  standards  of  known  titanium 
content. 

H.    METHOD   OF   BARNEBY  AND  ISHAM2 

The  weighed  sample,  0.4-0.6  gram,  is  moistened  in  a 
platinum  crucible  with  a  few  drops  of  water,  5-10  drops  of 
concentrated  sulphuric  acid  and  i  cc.  of  hydrofluoric  acid  are 
added.  The  crucible  is  heated  as  in  the  removal  of  silica  until 
the  complete  removal  of  sulphur  trioxide.  Five  grams  of 
sodium  carbonate  and  a  little  sodium  nitrate  are  added  and 
the  mixture  fused  for  30  minutes.  After  cooling,  the  crucible 
is  placed  in  a  beaker,  covered  with  hot  water,  and  heated  until 
the  melt  is  disintegrated.  The  residue  is  filtered  and  washed 
with  hot  water.  The  filter  is  perforated  and  washed  with 
hydrochloric  acid  (sp.  gr.  i.n)  into  a  clean  beaker,  and  any 
residue  in  the  crucible  is  dissolved  and  added  to  this  solution. 
The  beaker  is  heated  until  solution  is  complete  and  until  the 
volume  is  reduced  to  15-20  cc.  After  cooling  the  solution  is 
transferred  to  a  separatory  funnel,  the  beaker  being  washed 
with  hydrochloric  acid  (sp.  gr.  i.n).  An  equal  volume  of 
ether,  which  has  been  shaken  with  concentrated  hydrochloric 
acid,  is  added,  the  funnel  inverted  and  shaken,  releasing  the 
pressure  at  intervals  by  opening  the  stop-cock,  and  allowing 

1  U.  S.  Geol.  Survey,  Bulletin  422,  128. 

2  J.  Am.  Chem.  Soc.,  32,  957. 


IODIMETRIC  DETERMINATION  OF  COPPER  43 

the  liquid  carried  up  by  the  escaping  vapor  to  run  back  before 
closing  the  stop-cock.  The  funnel  is  allowed  to  stand  in  an 
upright  position  for  10  minutes,  and  then  the  aqueous  layer  is 
drawn  off  into  another  separatory  funnel.  The  ether  extract  is 
rinsed  twice  by  shaking  with  5-10  cc.  portions  of  hydrochloric 
acid  and  the  washings  added  to  the  aqueous  solution.  The 
extraction  with  ether  is  repeated  until  the  ether  layer  no  longer 
shows  the  greenish  tinge  of  dissolved  ferric  chloride.  The 
aqueous  solution  is  then  transferred  to  a  beaker,  10  cc.  of  con- 
centrated sulphuric  acid  are  added  and  the  solution  evaporated 
to  fumes  of  sulphur  trioxide.  The  cooled  solution  is  diluted 
to  about  100  cc.  and  nearly  neutralized  with  ammonia.  Two 
grams  of  ammonium  bisulphite  are  added  and  the  solution 
warmed  for  one-half  hour.  Ten  grams  of  ammonium  acetate 
and  5-10  cc.  of  glacial  acetic  acid  are  added  and  the  solution 
boiled  for  15  minutes.  Filter,  wash  with  dilute  acetic  acid, 
ignite  and  weigh  as  TiCV 

Notes.  —  i.  The  method  is  based  on  the  removal  of  silica 
with  hydrofluoric  acid,  the  removal  of  phosphates,  sulphates, 
and  aluminates  by  fusion  with  sodium  carbonate  and  extrac- 
tion with  hot  water,  and  the  removal  of  the  iron  by  extraction 
of  the  ferric  chloride  with  ether.  The  titanium  is  then  hydro- 
lyzed  as  in  the  preceding  method  hi  the  presence  of  an  acetate 
and  acetic  acid. 

IODIMETRIC   DETERMINATION   OF   COPPER 

MODIFIED   METHOD   OF  A.    H.    LOW1 

Standardization  of  Sodium  Thiosulphate  Solution.  —  Prepare 
a  solution  of  sodium  thiosulphate  by  dissolving  about  twenty- 
five  grams  of  the  salt  in  one  liter  of  water,  which  has  been 
recently  boiled  and  cooled  out  of  contact  with  the  air.  Weigh 
accurately  two  portions  of  about  0.25  gm.  of  pure,  clean  copper 
wire  into  250  cc.  Erlenmeyer  flasks,  and  dissolve  in  a  mixture 
of  5  cc.  concentrated  nitric  acid  and  25  cc.  of  water.  When 
solution  is  complete,  heat  to  boiling,  add  5  cc.  of  bromine  water 

1  J.  Am.  Chem.  Soc.,  24,  1082. 


44  QUANTITATIVE  ANALYSIS 

continuing  the  boiling  until  the  bromine  is  expelled.  Allow 
to  cool,  add  a  slight  excess  of  strong  ammonia,  and  boil  the 
solution  until  the  excess  has  been  driven  off,  adding  water 
occasionally  to  maintain  the  volume.  This  point  is  indicated 
by  the  change  in  color  of  the  solution,  or  by  a  slight  precipi- 
tation of  basic  copper  salt.  Add  a  few  cubic  centimeters  in 
excess  of  acetic  acid  and  boil  if  necessary  to  dissolve  any  basic 
copper  salt.  Cool  to  room  temperature,  add  three  grams  of 
potassium  iodide,  dissolved  in  a  small  amount  of  water,  and 
titrate  at  once  with  the  sodium  thiosulphate  solution.  When 
the  brown  color  of  the  iodine  has  become  weak,  add  enough 
starch  solution  to  give  a  distinct  blue  color,  and  finish  the 
titration-by  adding  sodium  thiosulphate  slowly  until  the  color 
due  to  the  free  iodine  has  completely  disappeared. 

Work  slowly  toward  the  end  point  and  stop  short  of  complete 
decolorization,  and  then  continue  only  when  the  liquid  after 
standing  a  minute  or  two,  still  persists  in  a  tinge  of  color. 

Procedure.  —  To  0.25-0.50  gram  of  finely  ground  ore  weighed 
into  a  250  cc.  Erlenmeyer  flask,  add  6  cc.  of  nitric  acid  (sp.  gr. 
1.42)  and  heat  gently  nearly  to  dryness.  Add  5  cc.  of  strong 
hydrochloric  acid  and  heat  again.  As  soon  as  the  incrusted 
matter  has  dissolved,  add  7  cc.  of  concentrated  sulphuric  acid 
and  heat  until  the  sulphuric  acid  fumes  freely.  Cool,  and  add 
25  cc.  of  water.  Then  heat  until  any  anhydrous  ferric  sul- 
phate is  dissolved,  and  filter  to  remove  insoluble  sulphates  and 
silica.  Wash  the  flask  and  filter  paper  until  the  volume  of  the 
filtrate  amounts  to  about  75  cc.,  receiving  it  in  a  No.  2  beaker. 
Place  on  its  edge  in  the  beaker  a  piece  of  sheet  aluminum, 
2  in.  x  6  in.,  bent  into  triangular  shape.  Cover  the  beaker  and 
boil  gently  for  seven  to  ten  minutes,  which  will  be  sufficient  to 
precipitate  all  the  copper  provided  the  solution  does  not  ex- 
ceed 75  cc.  Avoid  evaporating  to  very  small  bulk.  The 
aluminum  should  now  appear  clean,  the  copper  being  de- 
tached or  loosely  adhering.  Remove  from  the  heat  and  wash 
down  the  cover  and  sides  of  the  beaker  with  hydrogen  sulphide 
water.  Decant  the  liquid  through  a  filter  and  then  without 
delay  transfer,  by  means  of  a  jet  of  hydrogen  sulphide  water 


IODIMETRIC  DETERMINATION  OF   COPPER  45 

from  a  wash  bottle,  the  copper  to  the  filter,  leaving  the  foil  as 
clean  as  possible  in  the  beaker.  Wash  the  copper  and  filter 
thoroughly  with  hydrogen  sulphide  water,  being  careful  not 
to  allow  the  filter  to  stand  empty  until  the  washing  is  finished. 
Place  the  original  flask  under  the  funnel  and  pour  over  the 
aluminum  in  the  beaker  5  cc.  of  a  mixture  of  equal  parts  of  con- 
centrated nitric  acid  and  water.  Heat  just  to  boiling  and  pour 
the  hot  acid  very  slowly  upon  the  filter,  lifting  the  fold  if 
necessary.  Now,  before  washing,  pour  5  cc.  of  bromine  water 
into  the  filter  and  wash  the  beaker  and  filter  with  hot  water. 
Finally,  remove  the  filter  and  wash  any  residue  upon  it  into 
the  flask.  If  the  bromine  was  not  sufficient  to  give  a  slight 
tinge  to  the  filtrate  more  of  it  must  be  added.  Boil  the  nitrate, 
which  does  not  exceed  75  cc.  to  expel  the  excess  of  bromine  but 
do  not  concentrate  to  small  volume.  Remove  from  the  heat 
and  add  a  slight  excess  of  strong  ammonia  (usually  7  cc.). 
Boil  off  the  excess  of  ammonia  and  add  3  or  4  cc.  of  strong 
acetic  acid.  Cool  to  room  temperature,  add  three  grams  of 
potassium  iodide,  dissolved  in  a  small  amount  of  water  and 
titrate  with  thiosulphate  as  in  the  standardization. 

Notes.  —  i.  The  principle  of  this  method  is  based  upon  the 
fact  that  when  potassium  iodide  is  added  to  a  weakly  acid 
solution  of  a  copper  salt  iodine  is  liberated  according  to  this 
equation: 

2(CH3COO)2Cu  +  4KI  =  Cu2I2  +  4CH3COOK  + 12. 
The  iodine  is  then  made  to  react  with  standardized  sodium 
thiosulphate  according  to  the  reaction: 

2Na2S203  +  I2  =  aNal  +  Na2S,O6. 

2.  Copper  ores  contain  varying  amounts  of  silica,  sulphur, 
arsenic,  antimony,  lead,  silver  and  iron,  and  the  method  is  so 
designed  as  to  remove  or  render  these  elements  inert. 

Nitric  acid  is  the  best  solvent  for  sulphide  ores  and  in  order 
to  dissolve  oxides  of  iron,  remove  silver,  lead  and  silica  hydro- 
chloric and  sulphuric  acids  are  used  simultaneously.  Com- 
plete solution  of  anhydrous  ferric  sulphate  must  take  place 
previous  to  the  filtration  of  silica,  silver  chloride  and  lead 
sulphate. 


46  QUANTITATIVE  ANALYSIS 

3.  Aluminum   foil   precipitates   copper   from   its   solution 
quickly  and  completely  provided  the  proper  concentration  of 
acid  has  been  obtained.     In  addition  to  copper,  lead,  silver, 
bismuth,  arsenic  and  antimony  may  be  precipitated  if  present. 
Lead  should,  however,  have  been  almost  completely  removed 
as  insoluble  sulphate,  and  silver  as  chloride.     The  presence  of 
lead  and  bismuth  have  no  effect  upon  the  analysis  except  for 
a  slight  change  of  color  due  to  the  presence  of  their  slightly 
colored  iodides. 

Arsenic  and  antimony  would  interfere  if  allowed  to  remain 
in  the  lower  state  of  oxidation  by  reacting  with  the  liberated 
iodine.  Consequently  the  nitric  acid  solution  is  treated  with 
bromine  to  oxidize  these  elements  to  the  higher  state  of  oxida- 
tion. Bromine  also  oxidizes  any  nitrous  acid  which  might  be 
in  the  solution  as  the  result  of  the  reaction  between  copper  and 
nitric  acid. 

4.  Hydrogen  sulphide  water  is  used  not  only  to  precipitate 
traces  of  copper  left  in  solution,  but  also  to  prevent  oxidation 
of  finely  divided  copper. 

5.  The  addition  of  ammonia  and  acetic  acid  is  for  the 
purpose  of  regulating  the  hydrogen  ion  concentration.     In  the 
presence  of  strong  acids  there  is  danger  of  hydriodic  acid 
reducing  arsenic  and  antimonic  acids  with  the  liberation  of 
free  iodine.     This  reaction  takes  place  so  very  slowly  in  the 
weak  acid  solution  that  the  effect  is  negligible. 

The  presence  of  much  ammonium  acetate  interferes  with 
the  sharpness  of  the  end  point,  due  to  the  oxidizing  action  of 
iodine  upon  the  ammonia  from  the  hydrolyzed  ammonium 
acetate. 

6.  The  amount  of  potassium  iodide  added  is  in  excess  of 
that  required  for  0.50  gram  of  copper  and  consequently  should 
be  enough  to  take  care  of  all  ores  on  the  weight  of  sample 
specified.     The  reaction  proceeds  slowly  unless  an  excess  is 
present.     An  excess  beyond  a  certain  limit  has  no  effect  upon 
the  analysis,  and  this  excess  must  be  controlled  in  accordance 
with  the  volume  of  the  solution. 

The  reaction  takes  place  in  the  presence  of  sulphuric  and 
hydrochloric  acids  as  well  as  in  acetic  acid  solution,  but  on 
account  of  the  greater  hydrogen  ion  concentration  in  the  two 
former  acids,  the  volume  of  the  solution  must  be  more  care- 


PROXIMATE  ANALYSIS  OF  COAL          47 

fully  regulated  in  order  to  prevent  reaction  between  the  acid 
and  potassium  iodide.  Gooch  and  Heath1  have  studied  the 
effect  of  concentration  upon  this  reaction  for  sulphuric,  hydro- 
chloric, nitric  and  acetic  acids. 

7.  Standardized  solutions  of  sodium  thiosulphate  and  iodine 
are  both  fairly  stable  if  properly  prepared  from  pure  materials 
and  protected  from  light  and  heat.  Water  free  from  carbon 
dioxide  should  be  used  for  the  solution  of  the  sodium  thio- 
sulphate, otherwise  there  is  separation  of  free  sulphur.  Both 
solutions  should,  however,  be  frequently  checked  against  each 
other  and  against  some  standard.  Copper  is  used  in  this  case 
as  the  standard  as  it  is  easily  obtained  in  pure  form,  and  further 
it  reproduces  all  of  the  conditions  obtained  during  the  course 
of  the  analysis.  In  this  connection  it  is  well  to  refer  to  the 
method  given  on  page  83,  for  the  standardization  of  sodium 
thiosulphate. 


PROXIMATE   ANALYSIS   OF   COAL2 

Moisture.  —  A  one  gram  air-dried  sample  is  weighed  into  a 
shallow  porcelain  capsule  J  inch  deep  and  if  inches  in  diameter, 
and  heated  for  one  hour  at  105°  in  a  constant  temperature 
oven,  through  which  a  current  of  air,  dried  by  passing  through 
sulphuric  acid,  is  passing  at  a  rate  to  change  the  total  volume 
of  air  in  the  oven  two  to  four  times  a  minute.  The  covered 
capsule  is  cooled  in  a  desiccator  over  sulphuric  acid  and 
weighed.  The  loss  in  weight  is  called  "moisture  at  105°." 

Ash.  —  The  determination  is  made  upon  the  same  sample 
in  which  moisture  has  been  determined.  The  capsule  con- 
taining the  sample  is  heated  at  a  low  temperature  obtained  by 
placing  it  above  the  tip  of  a  flame  turned  down  to  2  or  3  inches 
in  height.  The  sample  should  be  stirred  frequently  with  a 
stout  nichrome  wire.  After  much  of  the  carbon  has  been 
burned  off  the  temperature  should  be  gradually  raised  to 
about  750°  C.  and  the  heat  continued  at  this  temperature  for 

1  Am.  J.  Set.  [4],  24,  67. 

2  Technical  Paper  76,  Bureau  of  Mines  1914;  Am.  Soc.  for  Testing  Materials 
(1914);  Bureau  of  Mines  Bulletin,  116;   Technical  Paper  133,  Bureau  of  Mines, 
1917. 


4»  QUANTITATIVE   ANALYSIS 

30  minutes,  or  until  all  of  the  carbon  is  burned  off.  Cool  in 
a  desiccator  and  weigh.  The  residue  represents  the  "un- 
corrected  ash." 

Volatile  Matter.  —  One  gram  of  coal  is  weighed  into  a  plati- 
num crucible  which  is  provided  with  a  tightly  fitting  per- 
forated nickel  cover.  The  crucible  is  placed  in  the  flame  of  a 
Meker  burner  and  heated  for  seven  minutes  at  950°  C.  After 
the  more  rapid  early  discharge  of  the  volatile  matter,  tap  the 
crucible  cover  so  as  to  seal  the  cover  and  crucible  more  per- 
fectly. The  temperature  should  be  determined  by  means  of 
a  thermo-couple  placed  through  the  cover,  and  touching 
lightly  upon  the  bottom  of  the  crucible.  Cool  the  crucible  in 
a  desiccator  and  weigh.  The  loss  in  weight  minus  the  moisture 
at  105°  C.  represents  the  volatile  matter. 

Fixed  Carbon.  —  The  fixed  carbon  is  obtained  by  subtracting 
the  sum  of  the  percentages  of  moisture,  ash  and  volatile  matter 
from  100. 

Sulphur.  —  Mix  thoroughly  on  glazed  paper  i  gram  of  coal 
and  3  grams  of  Eschka  mixture  (two  parts  of  magnesium  oxide 
and  one  part  of  sodium  carbonate),  transfer  to  a  porcelain 
crucible,  or  a  platinum  crucible,  and  cover  with  i  gram  of 
Eschka  mixture.  Heat  the  crucible  at  a  low  temperature  for 
30  minutes  with  an  alcohol  flame  or  in  an  electrically  heated 
muffle  furnace,  and  then  raise  the  temperature  to  about  925°  C. 
for  one  hour  or  until  all  of  the  black  particles  of  carbon  dis- 
appear. 

Transfer  to  a  300  cc.  beaker  and  digest  with  100  cc.  of  hot 
water  for  one-half  hour.  Filter,  wash  by  decantation  several 
times  and  finally  transfer  the  residue  to  the  filter  paper  and 
wash.  Treat  the  filtrate  amounting  to  about  250  cc.  with 
10  cc.  saturated  bromine  water,  acidify  slightly  with  hydro- 
chloric acid  and  boil  off  the  excess  of  bromine.  To  the 
boiling  solution  add  hot  dilute  barium  chloride  and  proceed 
as  in  the  determination  of  sulphur  in  pyrite. 

Notes.  —  i.  The  proximate  analysis  of  coal  originated  in 
response  to  a  demand  for  a  rapid,  fairly  accurate  method  for 
classifying  coals  for  industrial  purposes.  The  results  give 


PROXIMATE  ANALYSIS  OF  COAL  49 

important  data  as  to  the  commercial  value,  and  may  be 
obtained  in  very  much  shorter  time  than  the  results  of  an 
ultimate  analysis. 

2.  The  sampling  of  coal,  whether  at  the  mine  or  at  the  place 
of  destination,  is  a  very  important  matter,  and  the  subject  is 
too  extensive  to  be  dealt  with  here.     The  student  should  read 
on  this  subject  the  papers  referred  to  on  page  47. 

3.  The  loss  of  weight  at  105°  includes  not  only  that  moisture 
which  is  adsorbed  on  the  surface,  but  also  some  of  the  water 
which  is  an  essential  part  of  the  coal  itself.     Samples  may  have 
been  taken  from  a  wet  face  of  the  mine  or  from  a  car  which  had 
been  standing  in  the  rain  or  snow,  and  the  amount  of  this 
moisture  varies  with  the  weather  conditions.     It  is,  therefore, 
desirable  to  establish  nearly  normal  conditions  by  air-drying 
the  sample.     Coal  exposed  to  circulating  air  at  ordinary  tem- 
peratures will  either  give  up  or  take  on  moisture  depending 
upon  the  fineness  of  the  sample  and  the  humidity  of  the  air. 
A  point  of  equilibrium  is  always  reached  which  varies  with 
the  size  of  the  lumps  of  coal  exposed,  the  time  of  exposure 
and  the  humidity  of  the  air. 

The  inherent  moisture  or  water  of  constitution  varies  fairly 
constantly  with  the  district  from  which  the  coal  is  taken.  The 
coal  from  the  more  important  veins  of  the  Appalachian  field 
holds  about  2-4  per  cent  of  moisture;  that  from  the  western 
part  of  this  field,  in  Ohio,  varies  from  4-10  per  cent;  and  that 
from  the  Indiana  and  Illinois  field  varies  from  8-17  per  cent. 

The  commercial  value  of  a  coal  naturally  decreases  with  the 
increase  in  the  amount  of  moisture. 

4.  The  ash  of  a  coal  is  the  incombustible  residue  left  after 
all  of  the  carbonaceous  material  has  been  burned.     It  consists 
of  compounds  of  silica,  alumina,  calcium,  magnesium,  iron, 
and  the  alkali  metals,  and  is  derived  from  the  original  vegetable 
matter,  or  from  the  impurities  formed  during  the  formation 
of  the  coal  bed. 

The  amount  of  ash  in  a  coal  influences  its  commercial  value 
greatly,  as  the  efficiency  of  combustion  is  influenced  not  only 
by  the  amount  but  also  by  the  character  of  the  ash.  The 
fusibility  of  the  ash  is  also  an  important  factor,  and  there  is  a 
close  relationship  between  the  melting  point  of  the  ash  and  the 
tendency  to  clinker. 

1  Am.  Soc.for  Testing  Materials,  Standards,  1918,  673. 


50  QUANTITATIVE  ANALYSIS 

5.  The  volatile  matter  and  fixed  carbon  represent  respec- 
tively, the  gaseous  and  solid  material  which  are  capable  of 
being  utilized  by  heating  in  a  closed  space.     The  former 
consists  of  carbon  monoxide,  hydrogen,  methane  and  higher 
hydrocarbons,  and  the  non-combustible  gases,  carbon  dioxide 
and.  water  vapor.    The  composition  of  the  volatile  matter 
varies  greatly  with  the  source  of  the  coal,  and  the  amount 
varies  with  the  temperature  of  heating.     The  temperature  of 
heating,  950°,  is  purely  arbitrary  and  is  a  convenient  one  from 
the  analyst's  point  of  view.    There  is  greater  variation  in 
results  when  heating  at  low  temperatures  than  at  the  tempera- 
ture selected.     The  fixed  carbon  and  ash  represent  roughly  the 
amount  of  coke  which  may  be  obtained  from  any  coal. 

6.  Sulphur1  is  present  in  coal  as  pyrite  or  marcasite,  as 
sulphate  of  iron,  aluminum  or  calcium,  and  as  an  organic 
compound.     The   presence   of    much   pyrite   increases    the 
tendency  of  the  ash  to  clinker,  and  thus  decreases  the  com- 
mercial value  of  the  coal.     The  sulphur  present  as  an  organic 
compound  is  without  much  influence  except  that  it  lowers  the 
heating  value. 

7.  Eschka's  mixture  is  especially  valuable  in  the  oxidation 
of  sulphur  in  coal,  as  more  energetic  oxidizing  mixtures  would 
oxidize  the  carbon  with  explosive  violence.     Oxidation  of 
sulphur  in  coal  by  this  method  is  a  rather  slow  process,  but  a 
large  number  of  determinations  can  be  carried  on  simultane- 
ously without  much  attention. 

The  Eschka  mixture  may  also  be  applied  to  the  oxidation  of 
sulphur  in  mineral  sulphides  and  to  the  determination  of  sul- 
phur in  iron  and  steel. 

ANALYSIS  OF  PHOSPHOR-BRONZE 

DETERMINATION   OF   TIN 

Treat  0.5  gram  of  the  borings  in  a  No.  i  beaker  with  15  cc, 
HNOs  (sp.  gr.  i .  20) .  Evaporate  the  solution  on  the  water  bath 
or  steam  table  until  the  residue  is  just  dry,  and  remove  from  the 
heat  as  soon  as  this  stage  is  reached.  Prolonged  heating  of 
this  residue  must  be  avoided.  Treat  the  residue  with  a  mix- 
ture of  10  cc.  HNOs  (sp.  gr.  1.42)  and  50  cc.  water,  dividing  the 
acid  into  three  portions  and  boiling  and  decanting  after  each 

1  Technical  Paper,  254,  Bureau  of  Mines. 


ANALYSIS  OF   PHOSPHOR-BRONZE  51 

addition  through  a  9  cm.  hardened  filter  paper;  finally  com- 
plete the  washing  by  boiling  and  decanting  with  distilled  water 
until  the  metastannic  acid  is  apparently  free  from  copper. 
The  first  portion  of  filtrate  should  be  carefully  examined  for 
metastannic  acid,  refiltered  if  necessary,  and  each  successive 
clear  filtrate  should  be  removed  from  below  the  funnel  before 
more  wash  water  is  added,  as  the  precipitate  is  likely  to  run 
through  the  filter.  Preserve  the  filtrate  and  washings  for  the 
determination  of  lead  and  copper.  Leave  as  much  of  the  meta- 
stannic acid  as  possible  in  the  beaker  during  the  washing. 
When  the  washing  is  completed  and  the  filter  has  drained, 
remove  the  filter  from  the  funnel,  spread  it  out  upon  a  watch 
glass,  hold  it  vertically  above  the  beaker  containing  the 
residue,  and  wash  off  all  the  visible  residue  into  the  beaker, 
limiting  the  amount  of  water  as  far  as  practicable.  To  dis- 
solve the  small  amount  of  tin  remaining  in  the  filter,  spread 
on  the  bottom  of  a  beaker  and  pour  over  it  25  cc.  of  yellow 
ammonium  sulphide  solution  and  warm  gently  (covered)  for 
15  minutes.  Meanwhile  add  75  cc.  of  the  sulphide  solution 
to  the  metastannic  acid  in  the  beaker.  Pour  into  this  the 
sulphide  from  the  filter  and  wash  the  filter  three  times  with  hot 
water.  If  the  filter  is  perfectly  white  after  washing  out  the 
sulphide,  it  may  be  discarded;  otherwise  it  should  be  pre- 
served and  treated  as  directed  below.  Cover  the  beaker 
containing  the  sulphide  solution  and  digest  the  solution  on 
the  steam  table  at  a  low  heat  for  about  two  hours  with  occa- 
sional stirring.  Filter  off  the  copper  and  lead  sulphides, 
receiving  the  filtrate  in  a  600  cc.  beaker  and  wash  with  100  cc. 
of  dilute  ammonium  sulphide  (i  volume  ammonium  mono- 
sulphide  and  4  volumes  of  water).  Complete  the  washing 
with  water. 

Treat  the  filter  with  15  cc.  of  hot  HN03  (i  part  HN03  sp. 
gr.  i  .42  to  4  parts  water)  passing  it  through  the  filter  until  the 
sulphides  are  dissolved.  If  the  filter  treated  with  ammonium 
sulphide  was  preserved,  pass  the  same  hot  nitric  acid  solution 
through  that  filter  and  wash  both  filters  completely,  adding 
the  filtrates  and  washings  after  neutralization  with  ammonia 


52  QUANTITATIVE   ANALYSIS 

to  the  copper  and  lead  solution.  Smoke  off  the  filters  in 
a  weighed  porcelain  crucible  and  ignite  finally  at  a  high 
temperature,  weighing  the  residue  as  SnO2.  This  weight  is 
to  be  added  to  that  obtained  below. 

Dilute  the  ammonium  sulphide  solution  to  500  cc.,  make 
distinctly  acid  with  dilute  acetic  acid,  but  avoid  a  large  excess. 
Cover  the  beaker  and  allow  it  to  stand  in  a  warm  place  for 
three  to  four  hours,  or  over  night.  Decant  the  liquid  through 
a  filter,  pour  over  the  precipitate  150  cc.  water,  again  decant 
and  pour  over  it  150  cc.  of  dilute  ammonium  nitrate  solution 
(2  gms.  per  100  cc.  H^O  acidified  with  a  few  drops  of  acetic 
acid).  Again  decant  and  transfer  the  precipitate  to  the  filter, 
completing  the  washing  with  the  nitrate  solution.  Transfer 
the  moist  filter  and  precipitate  to  a  weighed  porcelain  crucible. 
Dry  and  smoke  off  the  filter  over  a  low  flame,  then  gradually 
raise  the  temperature  until  the  filter  burns  and  the  sulphur 
takes  fire.  Continue  the  gentle  heating  until  there  is  no  odor 
of  sulphur  dioxide,  and  then  increase  the  heat  gradually  until 
the  highest  heat  of  the  Tirrill  is  reached.  A  short  heating 
over  the  blast  lamp  is  advisable  before  final  weighing.  Ignite 
to  constant  weight.  Weigh  as  Sn02  and  report  as  metallic 
tin. 

Notes.  —  i.  The  phosphor  bronzes  are  essentially  alloys  of 
copper,  tin,  and  phosphorus,  but  they  may  also  contain  lead 
and  traces  of  other  elements.  They  are  characterized  by  their 
excellent  qualities  as  a  mechanical  constructive  material,  the 
small  effect  which  rise  of  temperature  has  upon  the  physical 
properties,  and  their  desirable  properties  for  bearings  for  high 
speed  machinery  and  fairly  heavy  loads.  For  bearings  they 
possess  a  low  coefficient  of  friction  and  are  hard  enough  to 
resist  abrasion.  They  may  be  classified  according  to  their 
mechanical  properties  into  two  groups:  (i)  the  malleable  phos- 
phor bronzes;  and  (2)  the  cast  phosphor  bronzes. 

The  malleable  phosphor  bronzes  are  those  in  which  the 
quantities  of  tin  and  phosphorus  are  relatively  small,  the  upper 
limits  of  which  may  be  taken  as  6  per  cent  of  tin  and  0.3  per 
cent  of  phosphorus.  The  malleability  is  due  to  the  fact  that, 
with  small  amounts  of  phosphorus,  copper  phosphide, 


ANALYSIS  OF  PHOSPHOR-BRONZE  53 

forms  a  homogeneous  solid  solution,  and,  further,  with  larger 
amounts  of  phosphorus,  the  tin  promotes  the  separation  of 
finely  divided  and  widely  disseminated  copper-copper  phos- 
phide eutectic.  Such  alloys  are  useful  for  wire,  gear  wheels, 
pinions,  bushings,  worm  wheel  rims,  etc. 

The  cast  phosphor  bronzes  are  particularly  suited  for  bear- 
ings. The  composition  of  such  alloys  varies  widely,  but  the 
upper  limits  of  tin  and  phosphorus  may  be  placed  respectively 
at  12  and  1.5  per  cent.  Lead  is  also  a  common  constituent  of 
these  bearing  metals  and  may  be  found  sometimes  to  the  extent 
of  10  per  cent.  These  alloys  show  on  microscopic  examination 
the  essential  structure  of  a  good  bearing  metal,  viz.:  a  hard 
crystalline  constituent  embedded  in  a  softer  plastic  matrix. 
The  load  is  carried  by  the  harder  material  while  the  plastic 
material  provides  for  continuous  lubrication.  The  presence 
of  lead  increases  the  amount  of  plastic  substance. 

2.  In  addition  to  the  elements  copper,  tin,  phosphorus  and 
lead,  bronzes  may  also  contain  antimony,  arsenic,  iron,  alu- 
minum, but,  inasmuch  as  most  of  the  commercial  bronzes  con- 
tain these  elements  only  in  traces,  a  special  method  has  not 
been  given  for  their  separation.     If  it  is  found  that  antimony 
is  present  and  it  is  desired  to  separate   and   determine   it, 
reference   should   be   made   for   details    to   Treadwell-Hall, 
Quantitative  Analysis.      The  principle  of  the  separation  is 
based  on  the  insolubility  of  antimony  sulphide  in  oxalic  acid 
solution  while  stannic  salts  are  not  precipitated.     Copper  and 
lead  are  also  held  in  small  amounts  in  the  residue  and  are  left 
as  sulphides  after  treatment  of  the  antimony  sulphide  with 
ammonium  polysulphide. 

3.  Evaporation  to  hard  dryness  of  the  metastannic  acid 
causes  it  to  lose  water,  and  results  in  making  it  quite  insoluble 
in  ammonium  polysulphide,   and  consequently  considerable 
care  should  be  exercised  at  this  point.     It  is  not  even  neces- 
sary to  evaporate  to  complete  dryness,  as  the  subsequent 
boiling  with  dilute  nitric  acid  will  cause  the  complete  separa- 
tion of  the  metastannic  acid. 

4.  Metastannic  acid  is  not  only  finely  divided  and  will 
pass  through  the  finest  filter  paper,  but  it  also  has  a  strong 
tendency  to  become  colloidal.     Boiling  the  residue  with  sepa- 
rate portions  of  dilute  nitric  acid  retards  the  formation  of 


54  QUANTITATIVE  ANALYSIS 

the  colloid  and  also  removes  small  amounts  of  copper  and  lead, 
which  are  carried  down  with  it.1 

5.  Stannic  sulphide  is  thrown  out  of  its  sulpho-stannate 
solution  with  acetic  acid,  rather  than  with  hydrochloric  or 
sulphuric  acids,  because  of  its  being  a  weaker  acid.    There  is, 
therefore,  less  danger  of  re-dissolving  the  sulphide  with  a 
slight  excess  of  acid. 

As  stannic  sulphide  is  slightly  soluble  in  solutions  containing 
hydrogen  sulphide  in  excess,  it  is  essential  to  allow  it  to  stand 
in  a  warm  place  until  all  hydrogen  sulphide  is  removed.  If 
this  precaution  is  neglected,  tin  will  appear  in  the  nitrate.  It 
is  always  advisable  to  test  this  nitrate  for  tin,  passing  hydrogen 
sulphide  into  the  boiling  solution. 

6.  The  stannic  sulphide,  if  washed  with  water,  becomes 
colloidal  on  the  removal  of  the  electrolytes  present  and  passes 
through  the  filter.     It  is  therefore  necessary  to  wash  with  an 
electrolyte   to   prevent  this.     Ammonium   nitrate  is   chosen 
because  it  leaves  no  residue  on  ignition,  and,  further,  it  helps 
appreciably  in  burning  the  filter  paper. 

7.  It  is  essential  to  heat  the  stannic  sulphide  at  a  low 
temperature  at  first  because  of  the  volatility  of  the  sulphide. 
The  burning  of  the  sulphur  furnishes  enough  heat.    As  soon 
as  the  sulphur  is  burned  off  the  temperature  may  be  raised 
without  danger.    Like  silica  and  titanic  oxide,  stannic  oxide 
loses  its  last  traces  of  moisture  only  at  the  temperature  of  the 
blast.    The  color  of  this  ignited  oxide  darkens  slowly  at  the 
higher  temperatures  and  usually  varies  in  color  from  a  light 
to  a  dark  gray. 

It  is  advisable  in  the  ignition  of  any  sulphide  to  oxide  to 
heat  with  dry  ammonium  carbonate  to  remove  traces  of 
sulphate  which  might  have  formed  during  the  ignition. 

DETERMINATION   OF   COPPER  AND   LEAD 

The  filtrate  from  the  metastannic  acid  should  not  exceed  in 
volume  200-250  cc.  To  determine  these  two  elements  the 
solution  is  subjected  to  electrolysis  until  both  have  been  com- 
pletely precipitated,  the  copper  as  metal  on  the  cathode,  the 

1  This  and  other  colloids  may  be  conveniently  coagulated  by  stirring  into  the 
solution  some  white  of  egg,  which  on  heating  will  coagulate  and  bring  down  with 
it  the  substance  which  it  is  desired  to  filter. 


ANALYSIS   OF   PHOSPHOR-BRONZE  55 

lead  as  hydrated  peroxide  on  the  anode.  For  this  purpose, 
clean  two  platinum  electrodes,  preferably  of  gauze,  by  immers- 
ing for  some  time  in  hot  dilute  nitric  acid,  washing  with  water 
and  then  with  alcohol.  Dry  at  130°  and  weigh.  Place  the 
electrodes  in  the  solution  making  the  smaller  the  cathode,  the 
larger  the  anode  and  begin  the  electrolysis  with  a  current  of 
0.25  ampere.  Continue  this  strength  current  from  4-6  hours,1 
and  then  reduce  to  o.i  ampere.  After  18-20  hours  the  elec- 
trolysis should  be  complete.  The  level  of  the  liquid  in  the 
beaker  should  be  raised  by  about  one-eighth  of  an  inch  by 
the  addition  of  water.  After  half  an  hour  an  observation 
should  be  made  to  see  whether  any  more  copper  has  been 
precipitated  on  the  clean  surface  of  the  wire  of  the  electrode. 
If  the  copper  has  been  completely  deposited,  the  wire  of  the 
cathode  will  remain  perfectly  bright  just  under  the  surface 
of  the  liquid.  If  any  copper  shows,  this  process  must  be 
repeated  until  it  has  all  been  removed  from  solution.  When 
complete  the  solution  should  be  siphoned  off  and  the  elec- 
trodes carefully  washed  with  distilled  water,  the  current  being 
allowed  to  pass  through  the  solution  during  the  process  of 
washing.  Before  disconnecting  the  electrodes  insert  a  wire 
between  the  binding  posts  so  as  not  to  cut  out  any  other 
solutions  in  the  same  circuit.  Immerse  the  copper  electrode 
in  water,  wash  with  alcohol,  dry  at  100°.  After  washing  the 
lead  peroxide  in  water,  dry  at  180°  C. 

The  lead  peroxide  does  not  adhere  as  firmly  to  the  electrode 
as  the  copper.  A  better  deposit  may  be  obtained  by  increas- 
ing the  surface  area  of  the  electrode,  and  by  having  a  matt 
surface.  If  any  peroxide  should  become  detached,  the  solu- 
tion is  decanted  away  from  it,  it  is  washed  with  water,  and 
then  by  means  of  alcohol  washed  on  to  a  weighed  watch  glass 
and  the  excess  of  alcohol  is  evaporated  off.  In  this  way  small 
quantities  of  lead  peroxide  can  be  conveniently  collected  and 
weighed. 

1  If  gauze  electrodes  are  available  the  current  may  be  increased  to  4-5 
amperes  so  as  to  bring  down  the  copper  and  lead  dioxide  very  much  more 
rapidly,  finishing  the  electrolysis  in  the  course  of  several  hours. 


.56  QUANTITATIVE   ANALYSIS 

Notes.  —  i.  In  nitric  acid  solution  of  copper  and  lead  salts, 
the  former  is  deposited  on  the  cathode  as  strongly  adhering 
metallic  copper,  and  the  latter  on  the  anode  as  hydrated  lead 
dioxide.  Various  views  have  been  expressed  to  account  for 
the  deposition  of  lead  as  peroxide  on  the  anode,  and  it  is  not 
certain  whether  lead  nitrate  hydrolyzes,  giving  rise  to  PbO2~ 
ion,  or  whether  a  similar  ion  is  formed  from  the  decomposition 
of  Pb(N03)4. 

2.  Lead  may  be  accurately  separated  from  copper  by  taking 
advantage  of  the  insolubility  of  lead  sulphate  in  dilute  sul- 
phuric acid,  but  the  simultaneous  separation  of  the  metals 
electrolytically  produces  results  just  as  accurate,   and  for 
•commercial  work  very  much  more  convenient.     The  separa- 
tion must  take  place  in  nitric  acid  solution  and  with  a  con- 
centration of  from  5  to  10  per  cent  by  volume  of  the  strong 
acid.     This  separation  is  not  applicable  in  presence  of  meta- 
stannic  acid,  as  both  copper  and  lead  dioxide  are  contaminated 
with  it. 

3.  The  time  for  electrolysis  seems  excessive,  but  where  a 
large  number  of  determinations  are  to  be  carried  out  from  day 
to  day  this  is  not  an  important  factor.     Increasing  the  current 
density  is  out  of  the  question  because  of  the  spongy,  non- 
adherent  deposits.     Stirring  the  solution  helps  some,  but  the 
most  efficient  aid  to  rapid  electrolysis  is  in  the  use  of  the 
rotating  cathode  or  anode.     By  this  process  the  solution  is 
not  only  stirred,  thus  constantly  bringing  fresh  solution  to  the 
electrode,  but  it  is  possible  to  obtain  adherent  deposits  with 
high  current  density.     The  rotating  cathode  was  proposed  by 
Gooch  and  Medway,1  and  the  rotating  anode  by  Exner.2     In 
each  case  the  electrode  was  rotated  at  high  speed  by  means  of 
a  small  motor.     Frary 3  proposed  in  place  of  the  motor  to  place 
the  solution  in  a  solenoid  and  thus  cause  a  rotation  of  the 
solution  itself.     Winkler 4  proposed  the  use  of  platinum  gauze 
electrodes,   but   the   advantages   were  not  recognized   until 
Stoddard  had  called  attention  to  their  use,  and  showed  that 
there  is  economy  of  platinum  and  time,  as  well  as  avoidance  of 

1  Am.J.Sci.  (4),  15, 320. 

2  /.  Am.  Chem.  Soc.,  25,  896. 

3  Zeit.  Electrochem,  1907,  308. 

4  Ber.,  32,  2192. 


ANALYSIS   OF   PHOSPHOR-BRONZE  57 

the  more  complicated  apparatus.  Stoddard1  has  obtained 
excellent  results  by  using  a  gauze  cathode.  He  operated  at 
higher  temperatures  and  used  heavier  currents  than  would  be 
possible  with  plate  electrodes,  and  reduced  the  time  of  opera- 
tion to  the  limit  of  the  rotating  apparatus. 

4.  Washing,  drying  and  weighing  of  the  deposited  copper 
must  be  carried  out  without  unnecessary  delay,  in  order  to 
prevent  oxidation.  By  careful  ignition  lead  dioxide  may  be 
quantitatively  converted  into  lead  monoxide. 


DETERMINATION   OF  PHOSPHORUS^   IN   PHOSPHOR-BRONZE 

Weigh  one  gram  of  the  borings  into  a  No.  2  beaker  and  dis- 
solve in  20  cc.  of  aqua  regia,  made  by  mixing  just  previous  to 
use  equal  volumes  of  the  concentrated  acids.  Have  the 
beaker  covered  with  a  watch  glass,  and  after  solution  is  com- 
plete heat  nearly  to  the  boiling  point  of  the  solution  for  fifteen 
minutes.  After  cooling  add  25  cc.  of  water,  and  then  just 
sufficient  ammonia  (sp.  gr.  0.90)  to  re-dissolve  all  of  the  copper 
hydroxide  and  to  produce  a  deep  blue  colored  solution.  Now 
add  50  cc.  colorless  ammonium  sulphide.  This  should  be 
enough  to  precipitate  the  sulphides,  and  the  supernatant 
liquid  should  show  no  blue  color.  If  it  does,  more  ammonium 
sulphide  should  be  added.  Digest  at  a  temperature  near  the 
boiling  point  of  the  solution  for  fifteen  minutes.  Allow  the 
precipitated  sulphides  of  copper  and  lead  to  settle,  filter  into 
a  300  cc.  Erlenmeyer  flask,  decanting  the  clear  liquid  carefully 
from  the  precipitate,  and  finally  throwing  the  precipitate  upon 
the  filter.  When  the  filter  has  drained  put  the  filter  and 
precipitate  back  into  the  beaker,  add  50  cc.  of  ammonium 
sulphide  wash  water  (one  part  colorless  ammonium  sulphide 
to  three  parts  water)  warm  and  stir  occasionally  for  ten 
minutes;  then  pour  the  whole  upon  another  filter,  wash  with 
50  cc.  of  ammonium  sulphide  wash  water  and  allow  it  to  drain 
completely.  The  total  volume  should  not  be  over  250  cc., 
but  it  is  not  necessary  to  evaporate  in  case  this  volume  is 

1  /.  Am.  Ghent.  Soc.,  31,  385. 

2  Dudley  and  Pease,  Eng.  and  R.  R.  Journ.,  March,  1894. 


58  QUANTITATIVE  ANALYSIS 

slightly  exceeded.  Add  to  the  filtrate  10  cc.  of  magnesia 
mixture  and  shake.  Place  the  flask  in  ice  water  and  allow 
to  stand  with  occasional  shaking  for  two  hours.  Filter  off 
the  precipitate  of  magnesium  ammonium  phosphate  upon  a 
small  filter  and  wash  with  ammonia  water  (one  part  0.96  sp. 
gr.  ammonia  to  three  parts  water)  until  nearly  free  from 
sulphide.  Pour  10  cc.  hydrochloric  acid  (one  part  HC1  sp. 
gr.  i.  20  to  four  parts  water)  into  the  flask,  taking  care  that  all 
of  the  precipitate  adhering  to  the  walls  of  the  flask  is  dissolved, 
and  then  pour  the  acid  through  the  filter,  allowing  the  solution 
to  run  into  a  No.  i  beaker.  Wash  the  flask  and  filter  with 
10  cc.  more  of  the  same  acid.  Add  3  cc.  of  magnesia  mixture 
to  the  nitrate,  and  then  add  ammonia  slowly  with  constant 
stirring  until  present  in  slight  excess.  Add  10  cc.  ammonia 
sp.  gr.  0.90,  allow  to  stand  in  ice  water  for  two  hours,  stirring 
the  solution  occasionally.  Filter,  and  wash  the  precipitate 
with  ammonia  water  until  free  from  chlorides,  and  ignite  with 
the  usual  precautions,  weighing  as 


Notes.  —  i  .  The  principle  of  this  determination  is  dependent 
upon  the  oxidation  of  phosphorus,  existing  in  the  alloy  as 
phosphide,  by  means  of  aqua  regia;  separation  of  lead  and 
copper  as  sulphides  by  means  of  ammonium  sulphide,  and 
after  filtration  the  precipitation  of  magnesium  ammonium 
phosphate  in  presence  of  ammonium  sulpho-stannate. 

2.  Complete  oxidation  of  the  phosphorus  cannot  be  accom- 
plished by  means  of  nitric  acid  alone,  although  many  of  the 
published  methods  are  based  on  the  quantitative  separation  of 
phosphorus  along  with  the  tin  in  the  residue  obtained  after 
treatment  with  nitric  acid.     This  process  leads  to  erroneous 
results,  as  some  of  the  phosphorus  always  remains  unoxidized. 
Treatment  with  aqua  regia  seems  necessary  for  complete 
oxidation. 

3.  Ammonia  is  added  previous  to  the  addition  of  ammonium 
sulphide  so  as  to  eliminate  any  unnecessary  separation  of 
sulphur.    It  forms  with  copper  the  complex  ion  Cu(NH3)4++. 
Lead  hydroxide  remains  undissolved  in  the  ammonia,  but  is 
converted  into  sulphide  by  ammonium  sulphide. 

4.  If  the  first  precipitate  of  magnesium  ammonium  phos- 


DETERMINATION  OF   CARBON  IN   STEEL  59 

phate  be  allowed  to  stand  too  long,  small  amounts  of  metallic 
sulphides  will  precipitate  with  it.  Shaking  and  standing  in 
ice  water  promotes  the  separation  of  magnesium  ammonium 
phosphate  and  lessens  the  danger  of  carrying  down  sulphides. 
The  second  precipitation  is  made  to  separate  from  traces  of 
sulphides  and  so  that  the  conditions  of  precipitation  may  be 
improved.  See  note  12,  page  27.  The  ignition  of  this 
precipitate  must  be  made  with  caution. 

DETERMINATION  OF  CARBON  IN  STEEL 
APPARATUS 

The  apparatus  necessary  for  the  direct  combustion  of  carbon 
consists  of  an  electrically  heated  furnace  with  suitable  rheo- 
stat, an  ammeter,  a  quartz  combustion  tube,  a  purifying  train, 
an  absorbing  train,  and  a  cylinder  of  compressed  oxygen. 

The  furnace  is  preferably  of  the  resistance  type  made  by 
winding  an  alundum  or  clay  tube  with  a  resistance  wire  such 
as  nichrome  and  surrounding  the  tube  with  insulating  material 
to  prevent  loss  of  heat.  The  length  of  the  furnace  should  be 
approximately  8  to  12  inches  and  it  should  have  an  opening 
capable  of  taking  a  quartz  tube  about  i|  inches  in  diameter. 
Suitable  furnaces  can  be  made  at  low  cost  and  several  types 
may  be  obtained  on  the  market  at  reasonable  cost.  A  tem- 
perature of  1000°  C.  must  be  obtained  without  danger  of 
burning  out,  and  must  be  maintained  for  a  long  period  of  time. 
A  suitable  furnace  running  on  a  no  volt-circuit  at  3!  to  4 
amperes  should  give  this  temperature.  Before  placing  the 
furnace  in  commission,  and  at  intervals  of  two  or  three  weeks 
it  should  be  calibrated  with  a  standard  thermocouple,  so  that 
the  operator  may  know  the  approximate  temperature  by  the 
ammeter  readings.  By  regulation  of  the  rheostat,  tempera- 
tures may  be  obtained  and  maintained  within  5  to  10  degrees 
of  that  desired. 

The  quartz  combustion  tube  should  be  about  24  inches  in 
length  and  i  inch  in  diameter.  It  should  be  glazed  on  the 
inner  surface.  Within  the  tube  should  be  placed  at  a  position 
corresponding  to  the  front  end  of  the  furnace  a  two-inch  roll 


60  QUANTITATIVE   ANALYSIS 

of  ignited  asbestos  wrapped  in  nichrome  gauze.  This  should 
be  left  permanently  in  place.  A  similar  roll  should  be  in- 
serted in  the  rear  of  the  tube  after  the  introduction  of  the  boat 
containing  the  sample.  These  rolls  serve  the  purpose  of 
protecting  the  rubber  stoppers  from  the  radiated  heat. 

In  the  center  of  the  tube  should  be  kept  a  cylinder  of  nickel 
foil  slightly  longer  than  the  combustion  boat  to  be  used.  This 
serves  the  purpose  of  protecting  the  walls  of  the  quartz  tube 
from  oxide  of  iron  formed  during  combustion. 

The  purifying  train  consists  of  a  1 2-inch  porcelain  tube 
f  inches  in  diameter  containing  granulated  copper  oxide,  and 
a  furnace  capable  of  heating  the  tube  to  a  dull  red  for  4  to  6 
inches  of  its  length.  Attached  to  this  tube  is  a  tower  con- 
taining fresh  soda-lime  and  this  in  turn  is  connected  with  the 
rear  end  of  the  combustion  tube  by  means  of  a  bubble  tube 
containing  a  small  amount  of  concentrated  sulphuric  acid. 

At  the  front  end  of  the  combustion  tube  there  is  connected 
a  bubble-tube  containing  granulated  zinc  and  attached  to  this 
is  a  U-tube  containing  granulated  calcium  chloride,  and  be- 
yond this  is  a  U-tube  or  one  of  the  many  improved  absorption 
tubes  filled  with  granulated  soda-lime,  or  a  special  mixture 
made  by  granulating  fresh  sodium  hydroxide  with  about  four 
times  its  volume  of  asbestos.2 

The  apparatus  is  shown  in  Fig.  i .  It  is  almost  unnecessary 
to  say  that  the  apparatus  should  be  tested  to  see  that  it  is 
perfectly  tight,  and  that  before  using  it  a  blank  should  be  run 
exactly  as  in  the  determination  itself. 

METHOD 

Weigh  2-3  grams  of  finely  divided  sample,  and  distribute  it 
evenly  over  the  surface  of  a  clay  or  alundum  boat  about  half 
rilled  with  RR.  Alundum.  Attach  an  absorption  tube  which 
has  previously  been  weighed  with  oxygen  in  it  from  the  blank 
determination.  Place  the  boat  containing  the  sample  within 
the  nickel  cylinder  in  the  center  of  the  heated  tube,  replace 
the  asbestos  plug,  connect  with  the  oxygen  supply  and  adjust 
the  rheostat  so  that  the  temperature  will  rise  rapidly  to  950- 
1000°.  Regulate  the  flow  of  oxygen  so  that  about  2-3  bubbles 

1  The  oxygen  supplied  commercially  is  so  pure  and  free  from  hydrocarbon 
vapors  that  this  part  of  the  train  may  be  omitted. 
2  J.  Ind.  'Eng.  Chem.,  13,  1052. 


DETERMINATION  OF  CARBON  IN  STEEL 


61 


per  second  pass  through  the  sulphuric  acid  bulb.  When  com- 
bustion begins  absorption  of  carbon  dioxide  will  take  place. 
Increase  the  flow  of  oxygen  slightly  during  the  next  one  or  two 
minutes.  After  combustion  is  complete  the  flow  should  be 
regulated  to  2-3  bubbles  per  second.  Continue  the  passage 
of  oxygen  for  5  minutes.  Disconnect  the  absorption  tube, 
stop  the  supply  of  oxygen,  and  place  the  absorption  tube  in 
the  balance.  The  increase  in  weight  represents  the  carbon 
dioxide. 


FIG.  i 


DETERMINATION   OF   GRAPHITE  IN  CAST  IRON 

Dissolve  i  gram  of  sample  in  35  cc.  of  nitric  acid  (sp.  gr. 
1.13),  boil  the  solution  from  5-10  minutes.  Filter  the  residue 
on  ignited  asbestos  in  a  small  carbon  funnel,  wash  several 
times  with  hot  dilute  potassium  hydroxide  solution  (sp.  gr. 
i.io),  followed  by  dilute  hydrochloric  acid,  and  finally  with 
hot  water.  Dry  at  100°  C.,  transfer  asbestos  and  graphite  to 
a  boat  and  burn  as  in  the  determination  of  total  carbon. 

Notes.  —  i.  Carbon  exists  in  irons  (>  1.70  per  cent  C.)  and 
steels  ( <  1.70  per  cent  C.)  in  four  forms;  Iron  Carbide,  known 
as  Cementite;  Hardening  Carbon;  Graphite;  Graphitic  Tem- 
per Carbon. 


62  QUANTITATIVE  ANALYSIS 

Iron  and  carbon  unite  to  form  a  carbide,  Fe3C,  which  is 
capable  of  being  held  in  solid  solution  (austenite)  the  limiting 
value  of  which  is  1.70  per  cent  carbon.  It  occurs  in  all  slowly 
cooled  (annealed)  carbon  steels,  and  in  irons  which  have  been 
chilled  in  passing  from  the  liquid  to  the  solid  state.  In  hypo- 
eutectoid  (<  0.85  per  cent  C.)  steels,  its  formation  takes  place 
on  passing  slowly  through  the  critical  temperature,  Ari,  at 
680°.  At  this  temperature  austenite  decomposes  into  a  iron 
and  cementite,  after  having  previously  thrown  out  some  of  its 
iron  (ferrite)  at  the  critical  temperature,  Ar3,  which  is  pro- 
gressively lowered  with  increase  of  carbon. 

In  hyper-eutectoid  (>  0.85  per  cent  C.)  steels  the  initial 
temperature  of  transformation  of  austenite  into  cementite 
rises  with  increasing  carbon  and  reaches  a  maximum  at  1.70 
per  cent  carbon  when  cementite  separates  at  1130°.  The  end- 
ing of  the  transformation  takes  place  at  the  same  temperature 
for  all  compositions  (0.85-1.70  per  cent  C.)  at  the  Ari  point. 

In  eutectoid  steels  (0.85  per  cent  C.)  complete  transforma- 
tion of  austenite  takes  place  at  Ari  into  an  intimate  mixture 
of  its  two  constituents,  iron  (ferrite)  and  cementite,  this  mix- 
ture being  known  as  pearlite.  Thus  hypo-eutectoid  steels 
contain  excess  ferrite  with  pearlite,  and  hyper-eutectoid  steels 
excess  cementite  and  pearlite. 

In  irons  of  hypo-eutectic  composition  (1.70-4.30  per  cent 
C.)  cementite  separates  at  1130°  as  part  of  the  eutectic  of 
austenite  and  cementite,  the  austenite  subsequently  trans- 
forms at  Ari  into  pearlite.  In  hyper-eutectic  (>  4.3  per  cent 
C.)  irons  the  initial  separation  of  cementite  rises  progressively 
with  increase  of  carbon  and  the  final  separation  takes  place 
at  1130°. 

These  facts  are  shown  in  the  iron  carbon  equilibrium  dia- 
gram, Fig.  2. 

On  slow  cooling  of  irons,  however,  the  above  conditions  are 
not  realized,  as  the  separated  iron  carbide  almost  immediately 
decomposes  into  graphite, 

Fe3C  ->  C  (graphite)  +  3Fe 

and  the  more  slowly  cooled  the  metal,  the  more  complete  is 
this  reaction. 

Dissolved  in  dilute  hydrochloric  or  sulphuric  acids,  steels 
containing  iron  carbide  evolve  hydrocarbons.  In  dilute  cold 


DETERMINATION  OF   CARBON  IN   STEEL 


nitric  acid  iron  carbide  separates  as  a  brown  flocculent  residue 
which  goes  into  solution  above  80°  and  gives  a  color  propor- 
tional to  the  amount  which  is  present  (Colorimetric  Method). 
The  elements  manganese,  sulphur  and  chromium  favor 
carbide  formation,  and  silicon,  phosphorus,  and  aluminum 
oppose  it  and  promote  graphite  formation.  Double  carbides 
are  formed  with  manganese,  chromium,  tungsten,  molybdenum 
and  vanadium. 


1520° 


900' 


Ar,  Final 
FerriW 


JSfO. 


FIG.  2 


The  effect  of  carbide  carbon  upon  the  physical  properties  of 
steel  is  shown  diagrammatically  in  Fig.  3-1 

Hardening  carbon  is  formed  when  a  steel  or  iron  is  quenched 
from  any  temperature  at  which  austenite  exists,  i.e.,  from 
above  Aci.  It  is  unstable  and  tends  to  pass  back  slowly  on 
tempering  (heating  below  Aci),  and  goes  over  completely  to 
carbide  carbon  by  heating  above  Aci  and  cooling  slowly. 

It  is  decomposed  by  hot  dilute  acids.    In  dilute,  cold  nitric 
acid  it  at  first  separates  as  an  insoluble  residue  and  then  goes 
into  solution  on  shaking.     The  solution  is  colored  in  propor- 
tion to  the  amount  of  hardening  carbon  present. 
1  J.  H.  Nead,  Am.  Inst.  Min.  Eng.  (1916),  2341. 


64 


QUANTITATIVE   ANALYSIS 


Graphitic  temper  carbon  is  produced  by  heating  irons  rich 
in  cementite  which  decomposes  at  about  1000°  into  iron  and 


EFFECT  OF  CARBON  ON    PHYSICAL  PROPERTIES 
Heat  Treatment -Annealed  just  above  Ac8 

A — Tensile  Strength 

B — Elastic  Limit   Yield  Point 

C  — Elongation 

D — Contraction  of  Area 


.80  1.00 

Per  cent— Carbon 

FIG.  3 


1.20 


graphitic  temper  carbon  (Malleableizing  Process),  and  it  is 
sometimes  formed  in  annealing  high  carbon  steels. 

Both  graphite  and  graphitic  temper  carbon  are  unaffected 
by  boiling  dilute  acids.  Boiling  concentrated  nitric  acid 
oxidizes  them  only  very  slowly.  In  oxygen,  the  amorphous 


DETERMINATION  OF   MANGANESE  IN   STEEL  65 

graphitic  temper  carbon  is  burned  more  readily  than  the 
crystalline  graphite. 

2.  The  carbon  in  plain  carbon  steels  is  completely  burned 
at  a  temperature  of  950-1000°  C.     In  some  alloy  steels  — 
chrome-nickel,    chrome- tungsten,    chrome- vanadium  —  com- 
plete combustion  does  not  take  place  below  1050-1100°  C.,  and 
on  this  account  a  flux,  Pb304,  is  sometimes  used,  but  it  is  pref- 
erable to  burn  direct  if  the  temperature  can  be  obtained. 
Another  method  employed  to  burn  the  alloy  steels  is  to  mix 
with  them  a  known  weight  of  a  low  carbon  iron,  such  as  Armco 
Ingot  Iron. 

3.  Instead  of   using  potassium  hydroxide  as  absorbent, 
some  workers  prefer  soda-lime,  or  barium  hydroxide.    If  the 
latter  is  used  the  determination  may  be  finished  volumetrically 
by  (i)  filtering  the  precipitated  barium  carbonate  and  titrating 
the  excess  barium  hydroxide,  or  (2)  by  dissolving  the  filtered 
barium  carbonate l  in  excess  standard  acid  and  titrating  for 
the  excess. 

4.  The  whole  apparatus  should  be  tested  to  see  that  there 
is  no  leakage  of  gas  before  proceeding  with  any  determination. 
After   having   assembled   the   apparatus,   and  having  been 
assured  of  its  being  tight,  a  blank  determination  should  be 
made  exactly  as  in  the  regular  determination.    The  increase 
in  weight  of  the  absorption  tube  should  not  amount  to  more 
than  3  milligrams. 

5.  There  is  always  difficulty  in  weighing  accurately  any 
piece  of  glass  having  a  large  surface  area  on  account  of  the 
variations  in  the  amount  of  condensed  moisture.     On  this 
account  it  is  always  necessary  to  verify  the  weight  of  the 
potash  bulb  before  beginning  a  day's  work,  and  it  is  never 
allowable  to  assume  the  last  weight  of  the  day  before.    The 
bulb  should  always  be  wiped  with  a  clean,  dry  cloth  after 
handling  and  before  being  placed  in  the  balance  case. 

Some  of  the  soda-lime  bulbs  have  small  surface  area  and 
have  a  very  considerable  advantage  in  this  respect  over  the 
potash  bulbs. 

DETERMINATION  OF  MANGANESE  IN  STEEL 

VOLHARD  METHOD 

Standardization   of  Potassium   Permanganate   Solution.  — 
Standardize  the  potassium  permanganate  solution  in  the  follow- 

1  Cain,  J.  Ind.  Eng.  Chem.,  6,  465. 


66  QUANTITATIVE  ANALYSIS 

ing  manner.  From  a  burette  measure  into  a  500  cc.  Florence 
flask  several  portions  of  about  25  cc.  each  of  a  manganous 
chloride  solution,1  the  value  of  which  has  been  very  accurately 
established  according  to  the  method  given  on  page  17.  Add 
20  cc.  zinc  nitrate  solution  (300  grams  Zn(NO3)2,6H2O  per 
liter),  dilute  with  hot  water  to  about  300  cc.,  add  two  or  three 
drops  of  dilute  nitric  acid,  and  heat  to  near  the  boiling  point. 
Now  add  rapidly  nearly  as  much  permanganate  solution  as  it 
is  thought  will  precipitate  all  of  the  manganese.  Rotate  the 
solution  thoroughly;  and  then  add,  cautiously,  enough  per- 
manganate solution  to  give  a  permanent  color  to  the  super- 
natant liquid. 

METHOD 

For  steels  containing  about  one  per  cent  of  manganese 
weigh  a  three-gram  sample;  for  higher  percentages  of  manga- 
nese use  a  correspondingly  lower  weight.  Place  the  borings 
in  a  porcelain  casserole  and  treat  with  30  cc.  of  nitric  acid 
(sp.  gr.  i. 20).  When  solution  of  the  metal  is  complete  raise 
the  watch  glass  by  supporting  it  on  a  glass  triangle,  and 
evaporate  to  dryness.  Then  remove  the  watch  glass  and 
carefully  bake  the  contents  of  the  dish  until  no  more  oxides 
of  nitrogen  are  evolved.  After  the  casserole  has  cooled,  add 
20  cc.  concentrated  hydrochloric  acid  and  heat  until  all  ferric 
oxide  is  converted  into  chloride.  (If  cast  iron  is  being  analyzed, 
the  solution  should  be  evaporated  to  dryness,  taken  up  in 
hydrochloric  acid,  and  the  graphite  and  dehydrated  silica 
filtered  off.)  Concentrate  the  solution  to  remove  the  excess 
acid  and  transfer  it  to  a  500  cc.  calibrated  flask,  and  dilute  to 
about  200  cc.  Now  add,  cautiously,  strong  sodium  carbonate 
solution  a  little  at  a  time  until  the  precipitate  just  redissolves 
and  the  solution  becomes  colored  deep  red.2  Then  add 
slowly  in  small  amounts  zinc  oxide  suspended  in  water, 
shaking  the  flask  after  each  addition,  and  continue  this 
process  until  a  point  is  reached  where  the  ferric  hydroxide 

1  Six  grams  of  the  crystallized  salt  dissolved  in  one  liter  of  water. 
1  Compare  Spathic  Iron  Ore  Procedure. 


DETERMINATION  OF  MANGANESE  IN  STEEL  67 

suddenly  coagulates.  Allow  the  precipitate  to  settle,  and  fill 
the  flask  with  water  exactly  to  the  graduation  mark.  Mix 
the  contents  of  the  flask  thoroughly  by  pouring  back  and  forth 
into  a  dry  beaker  several  times.  Allow  the  mixture  to  settle, 
and  then  filter  through  a  four-inch  dry  filter  paper.  Collect 
250  cc.  of  the  filtrate,  after  the  rejection  of  the  first  five  cubic 
centimeters,  in  a  graduated  flask.  Transfer  this  solution  to 
a  500  cc.  Florence  flask,  add  two  drops  of  dilute  nitric  acid, 
heat  to  near  the  boiling  point,  and  titrate  with  potassium 
permanganate  to  pink  color,  exactly  as  in  the  standardization. 

Notes.  —  i.  Manganese  exists  in  ordinary  steels  in  the  form 
of  a  solid  solution  with  iron.  Small  amounts  are  also  present 
in  the  forms  of  manganese  sulphide,  MnS,1  and  manganese 
silicate,  M^SiaOs,2  which  form  part  of  the  slag  found  in  steels. 
In  manganese  steels,  ferro-manganese  and  spiegeleisen  there 
is,  in  addition  to  the  solid  solution,  some  manganese  as  carbide, 
Mn3C2,  or  as  a  double  manganese-iron  carbide.  Manganese 
is  primarily  put  in  steel  for  the  purpose  of  deoxidizing  and 
desulphurizing  the  melt,  so  as  to  prevent  "red  shortness"  or 
brittleness  during  the  forging  heats.  Some  excess  always 
appears  in  the  finished  product,  and  in  commercial  steels  is 
found  in  amounts  varying  from  0.2  to  about  i.oo  per  cent.  In 
such  amounts  it  increases  the  strength  and  hardness  and 
decreases  somewhat  the  ductility.  These  effects  are  more 
pronounced  in  high  carbon  steels  than  in  low  carbon  material. 

In  metals  containing  manganese  in  excess  of  i  per  cent  the 
hardness  and  brittleness  increase  rapidly  and  reach  a  maxi- 
mum between  5  and  6  per  cent.  In  such  products  the  hard- 
ness and  brittleness  are  so  great  that  it  is  impossible  to  machine 
them  with  any  tool.  Beyond  7  per  cent  of  manganese  there 
is  a  progressive  increase  in  the  ductility,  and  steels  containing 
about  13  per  cent  manganese  are  characterized  by  great 
strength,  toughness  and  high  ductility.  Such  steels  are  known 
as  manganese  steels  and  have  found  extensive  application  in 
the  industries. 

Manganese  lowers  the  critical  temperature,  An.     With  in- 

1  Osmond  and  Werth,  Annales  des  Mines,  1885. 
8  Stead,  Iron  and  Steel  Magazine,  9,  105. 


68  QUANTITATIVE  ANALYSIS 

creasing  percentages  of  manganese  the  critical  temperature 
finally  falls  below  the  ordinary  room  temperature,  and  self- 
hardening  steels  result.  See  notes  on  Carbon,  page  61. 

2.  The  principle  of  the  Volhard  method  is  based  upon  the 
reaction 

2KMnO4  +  3MnSO4  +  2H2O  =  5MnO2  +  2KHS04  +  H2S04. 
That  is,  when  potassium  permanganate  is  added  to  a  neutral 
manganous  salt,  all  of  the  manganese  in  the  latter  is  oxidized 
to  the  dioxide  and  the  permanganate  is  reduced  to  the  dioxide. 
The  reaction  never  takes  place  exactly  as  represented  in  the 
equation,  except  in  the  presence  of  a  few  drops  of  nitric  acid 
and  the  salt  of  some  heavy  metal.  In  the  absence  of  these 
substances  the  manganese  is  not  oxidized  completely  to  Mn02. 
This  is  provided  for  in  the  standardization  by  the  addition  of 
zinc  nitrate  solution,  and  in  the  determination  by  the  reaction 
of  the  ferric  sulphate  with  the  zinc  oxide. 

Fe2(S04)3  +  3ZnO  +  3H2O  -  2Fe(OH)3  +  3ZnSO4. 

3.  Since  two  molecules  of  potassium  permanganate   will 
oxidize  three  atoms  of  manganese,  and  since,  in  acid  solutions, 
the  same  amount  of  permanganate  will  oxidize  ten  atoms  of 
iron,   it  follows  that   icFe  is  equivalent  to  3Mn.     Having 
established  the  value  of  the  permanganate  solution  in  terms  of 
iron  or  sodium  oxalate,  it  would  be  a  simple  matter  to  calculate 
its  value  in  terms  of  manganese.     This  calculation  should  be 
made  so  as  to  check  the  value  obtained  by  titrating  against 
manganous  sulphate,  but  the  latter  value  should  be  used  on 
account  of  its  having  been  obtained  under  exactly  the  same 
conditions  as  in  the  actual  determination.    The  difference 
between  the  two  values  is  usually  extremely  small. 

4.  In  the  standardization,  and  also  in  the  actual  titration, 
it  is  impossible  to  add  an  excess  of  potassium  permanganate 
and  then  to  titrate  back  with  manganous  sulphate  solution, 
on  account  of  the  fact  that  manganese  dioxide  reacts  catalyti- 
cally  with  permanganic  acid,1  which  liberates  oxygen  accord- 
ing to  the  following  equation: 

2HMn04  =  H20  +  2MnO2  +  3O, 

thus  losing  three-tenths  of  the  oxygen  which  should  have  been 
used  in  oxidizing  manganese  sulphate. 

1  Morse,  Hopkins  and  Walker,  Am.  Chem.  /.,  18,  401. 


DETERMINATION  OF   MANGANESE  IN  STEEL 


5.  The  Volhard  method  is  particularly  well  adapted  for 
the  determination  of  manganese  in  those  products  where  the 
manganese  content  is  high,  i.e.,  above  i  per  cent.  With  lower 
content  than  0.50  per  cent  there  is  difficulty  in  getting  a  satis- 
factory separation  of  manganese  dioxide  without  unduly 
increasing  the  weight  of  sample. 

The  method  is  not  applicable  to  the  analysis  of  chrome  steels 
as  the  zinc  oxide  may  precipitate  chromium  only  incompletely, 
in  which  case  it  might  be  oxidized  by  the  potassium  perman- 
ganate. Cobalt  and  vanadium  interfere  in  a  similar  manner. 

In  steels  rich  in  nickel  it  is  difficult  to  obtain  a  satisfactory 
end  point. 

WILLIAMS   METHOD1 

Weigh  two  three-gram  samples  into  750  cc.  Erlenmeyer 
flasks  and  cover  with  100  cc. 
nitric  acid  (sp.  gr.  1.42). 
Place  the  flask  covered  with 
a  small  watch  glass  on  the 
steam  table  and  allow  it  to 
remain  until  solution  is  com- 
plete. As  the  steel  becomes 
passive  on  treatment  with 
strong  nitric  acid,  it  is  of 
little  advantage  to  try  to 
hurry  the  solution  by  boil- 
ing. When  the  steel  is  com- 
pletely dissolved,  add  three 
grams  of  potassium  chlorate, 
and  after  five  minutes  add 
a  second  portion  of  three 
grams,  heating  on  the  steam 
table  during  this  time.  Af- 
ter ten  minutes  remove  from 
the  steam  table  and  heat  for  FlG 

five  minutes  in  a  hood  with 
good  draught  until  the  excess  chlorine  dioxide  is  driven  off. 

1  Trans.  Am.  Inst.  Min.  Eng.,  10,  100. 


70  QUANTITATIVE   ANALYSIS 

Cool,  and  filter  without  undue  delay  on  asbestos  which  has 
been  previously  treated  with  dilute  hydrochloric  acid  and 
washed  with  water  until  the  asbestos  does  not  reduce  dilute 
potassium  permanganate  solution.  The  asbestos  should  be 
placed  on  a  platinum  spiral,  a  few  pieces  of  glass  tubing,  or 
some  glass  beads  in  the  bottom  of  a  manganese  funnel.  When 
the  excess  of  nitric  acid  has  drained  off,  place  a  clean  beaker 
under  the  funnel,  begin  to  wash  with  water,  and  continue 
until  litmus  paper  shows  no  test  for  nitric  acid.  Then  wash 
the  manganese  dioxide  and  asbestos  back  into  the  flask  in 
which  the  precipitation  was  made. 

Add  50  cc.  ferrous  sulphate  solution  (50  cc.  H^SCX  sp.  gr. 
1.84;  5  grams  FeSO^H^O;  450  cc.  H2O)  the  value  of  which, 
in  terms  of  potassium  permanganate,  has  recently  been  es- 
tablished. Dilute  to  200  cc.  with  water.  Shake  until  the 
manganese  dioxide  has  completely  dissolved,  and  titrate  to 
pink  color  with  potassium  permanganate. 

Notes.  —  i.   The  principle  of  this  method  is  based  upon  the 
two  reactions: 

Mn(N03)2  +  2HC103  =  MnO2  +  2C1O2  +  2HNO3. 

2FeS04  +  2H2SO4  =  MnSOi  +  Fe2(SO4)3  +  2H20. 


The  oxidation  of  manganous  nitrate  to  dioxide  will  take 
place  only  in  concentrated  nitric  acid  solution.  Dilute  nitric 
acid  may  be  used  to  dissolve  the  steel,  but,  if  used,  the  solution 
must  be  concentrated  before  adding  the  potassium  chlorate, 
otherwise  incomplete  oxidation  will  result. 

Since  one  molecule  of  manganese  dioxide  will  oxidize  two 
molecules  of  ferrous  sulphate  it  is  evident  that  one  manganese 
is  equivalent  to  two  atoms  of  iron.  This  ratio  is  used  in  the 
calculations,  and  the  iron  value  of  the  potassium  permanganate 
is  taken  as  the  standard.  The  manganese  value  of  the  potas- 
sium permanganate  in  the  Williams  method  should  be  five- 
thirds  of  the  strength  found  in  the  Volhard  method. 

2.  This  method  is  well  adapted  to  the  determination  of 
manganese  in  steels  containing  not  more  than  0.75  per  cent  of 
that  element.  With  higher  amounts  the  filtration  of  the 
dioxide  becomes  more  and  more  difficult  unless  the  size  of  the 


DETERMINATION  OF  MANGANESE   IN   STEEL  71 

sample  is  correspondingly  decreased,  and,  further,  there  is  an 
increasing  error  with  an  increase  in  the  amount  of  manganese 
dioxide  precipitated.  As  the  precipitate  is  not  absolutely 
pure  MnO2,  but  contains  slightly  less  oxygen  than  represented 
by  the  formula,  it  will  be  seen  that  the  error  increases  with  the 
amount  of  dioxide  thrown  out  of  solution. 

As  the  precipitate  loses  oxygen  slowly  on  standing,  it  is 
important  to  filter  as  soon  as  possible  after  precipitation. 

The  method  is  not  especially  well  adapted  to  cast  irons 
on  account  of  the  difficulties  of  filtration  in  the  presence  of 
graphite  and  gelatinous  silica. 

3.  Care  should  be  exercised  in  the  addition  of  potassium 
chlorate.     If  added  to  a  boiling  solution  dangerous  explosions 
may  result. 

4.  Some  asbestos,  either  because  of  its  containing  ferrous 
iron  or  organic  matter,  reduces  potassium  permanganate.     It 
is,  therefore,  necessary  to  test  each  new  lot  to  see  whether  or 
not  it  will  react  with  very  dilute  permanganate  solution. 
This  difficulty  might  be  obviated  by  passing  the  reducing 
solution,  ferrous  sulphate,  or  oxalic  acid,  through  the  funnel 
containing  the  manganese  dioxide,  but  it  is  much  simpler  to 
avoid  the  washing  this  would  involve  by  putting  the  dioxide 
and  asbestos  into  the  reducing  solution. 

5.  Almost  any  standard  reducing  solution  may  be  used  to 
react  with  manganese  dioxide.     Ferrous  sulphate  and  oxalic 
acid  are  the  most  commonly  used.     Ferrous  sulphate  in  acid 
solution  is  fairly  stable  and  has  the  very  distinct  advantage  of 
reacting  in  the  cold.     Oxalic  acid  reacts  only  when  warmed  and 
has  the  disadvantage  of  changing  concentration,  unless  steril- 
ized, because  of  organic  growth  in  the  solution. 

Whatever  the  reducing  solution  used,  a  blank  should  be 
made  before  each  day's  work  against  the  standard  potassium 
permanganate. 

6.  It  is  impossible  to  ignite  the  precipitated  dioxide  and 
weigh  as  Mn3O4,  because  of  the  occluded  iron  and  the  indefinite- 
ness  of  composition  of  the  ignited  oxide.     Provision  may  be 
made  for  the  separation  of  the  iron,  and  the  determination  may 
be  finished  as  given  on  page  17. 

7.  The  method  is  applicable  in  the  presence  of  all  the  con- 
stituents of  the  more  common  steels. 


72  QUANTITATIVE  ANALYSIS 

THE   BISMUTHATE   METHOD  FOR  MANGANESE 

Weigh  into  a  250  cc.  Erlenmeyer  flask  about  one  gram  of 
borings  and  treat  with  50  cc.  of  nitric  acid1  (sp.  gr.  1.13). 
Heat  until  solution  is  complete,  allow  to  cool,  and  then  add 
about  0.5  gram  of  sodium  bismuthate.  Rotate  the  contents 
of  the  flask,  and  heat  until  the  pink  color  has  disappeared. 
If  the  solution  shows  precipitated  manganese  dioxide,  add 
crystals  of  ferrous  sulphate,  free  from  manganese,  until  it 
becomes  clear.  Heat  for  two  minutes  to  remove  oxides  of 
nitrogen,  and  cool  to  about  15°.  Now  add  2  to  3  grams  of 
sodium  bismuthate,  and  agitate  the  contents  of  the  flask  for 
several  minutes.  Dilute  with  50  cc.  of  three  per  cent  nitric 
acid,2  and  filter  through  asbestos,  as  prescribed  in  the  previous 
method,  into  a  300  cc.  Erlenmeyer  flask.  Wash  the  asbestos 
with  50  to  100  cc.  of  cold  three  per  cent  nitric  acid.  Run  into 
this  solution  50  cc.  of  the  ferrous  sulphate  solution  which  was 
used  in  the  Williams  method,  and  titrate  back  to  pink  color 
with  standard  potassium  permanganate. 

The  value  of  the  ferrous  sulphate  solution  in  terms  of 
potassium  permanganate  must  be  determined  in  the  following 
manner.  Measure  into  a  250  cc.  Erlenmeyer  flask  50  cc.  of 
cold  nitric  acid  (sp.  gr.  1.13),  add  about  0.5  gram  of  sodium 
bismuthate,  agitate,  and  filter  through  asbestos.  Dilute  with 
50  cc.  of  cold  three  per  cent  nitric  acid,  run  in  50  cc.  of  ferrous 
sulphate  solution,  and  titrate  with  permanganate  solution  to 
pink  color. 

Having  determined  the  value  of  the  permanganate  solution 
in  terms  of  ferrous  sulphate,  the  manganese  in  the  sample  is 
represented  by  the  difference  between  the  amounts  of  per- 
manganate solution  actually  used  in  the  determination  and 
in  the  titration  of  a  volume  of  ferrous  sulphate  equivalent  to 
that  used  in  the  determination. 

Notes.  —  i.   The  method  originated  with  Schneider,3  who 
used  bismuth  tetroxide  as  the  oxidizing  agent.     This  oxide  is 

1  One  volume  HNOs  sp.  gr.  1.42;  three  volumes  H2O. 
*  30  cc.  of  HNOs  (sp.  gr.  1.42)  to  one  liter  of  water. 
3  Dingier' s  Polytech.  J.,  269,  224. 


DETERMINATION  OF  MANGANESE  IN  STEEL  73 

very  difficult  to  prepare  free  from  chlorides,  and,  as  traces  of 
hydrochloric  acid  interfere  with  the  sharpness  of  the  end  point, 
it  was  abandoned  by  Reddrop  and  Ramage,1  who  proposed  the 
use  of  sodium  bismuthate.  More  recently  the  method  has 
been  studied  and  recommended  by  Blair 2  and  by  Blum.3 

Sodium  bismuthate  is  supposed  to  be  the  sodium  salt  of  the 
hypothetical  bismuthic  acid,  HBiOa.  The  product  sold  under 
this  name  is  probably  of  indefinite  and  variable  composition. 

2.  The  method  is  based  upon  the  fact  that  sodium  bis- 
muthate oxidizes  a  manganous  salt  in  the  cold  to  permanganic 
acid,  which  can  be  reduced  by  ferrous  sulphate  the  value  of 
which  is  known  in  terms  of  standard  potassium  permanganate. 
Ferrous  sulphate  is  not  readily  acted  upon  by  cold  nitric  acid 
and  can  consequently  be  used  to  reduce  the  permanganic  acid 
without  introducing  an  error. 

Lead  peroxide  oxidizes  manganese  to  permanganic  acid  in 
hot  solution,  but  the  results  are  not  reliable  when  more  than 
two  per  cent  of  manganese  is  present.  In  hot  solution  per- 
manganic acid  oxidizes  some  of  the  manganous  nitrate  to 
dioxide. 

3.  Since  two  molecules  of  permanganic  acid  will  give  up 
five  atoms  of  oxygen,  it  follows  that  it  will  oxidize  ten  atoms 
of  iron. 

Hence 

2HMnO4  =  loFe, 
iMn  =  5Fe. 

From  these  equations  it  can  be  seen  that  the  value  of  the 
standard  potassium  permanganate  may  readily  be  obtained  in 
terms  of  manganese  from  the  iron  standard. 

The  value  may  be  determined  directly  in  terms  of  man- 
ganese by  using  a  definite  volume  of  standard  manganous 
sulphate  solution.  This  solution  may  be  oxidized  and  deter- 
mined by  the  bismuthate  process,  exactly  as  described  in  the 
procedure. 

4.  The  addition  of  a  small  amount  of  sodium  bismuthate  to 
the  hot  solution  is  to  oxidize  the  hydrocarbons  formed  by  the 
decomposition  of  iron  carbide.    The  excess  bismuthate  is 

1  J.  Chem.  Soc.,  67,  268. 

2  /.  Am.  Chem.  Soc.,  26,  33. 

8  J.  Am.  Chem.  Soc.,  34,  1379. 


74  QUANTITATIVE  ANALYSIS 

rapidly  decomposed  by  the  hot  nitric  acid,  and  then  the  latter 
reacts  with  the  permanganic  acid,  precipitating  manganese 
dioxide.  This  in  turn  is  reduced  by  the  addition  of  a  small 
amount  of  ferrous  sulphate.  , 

5.  It  is  stated  that  chromium  in  small  amounts  does  not 
interfere  with  this  method,  but  this  is  contrary  to  the  author's 
experience.     For  accurate  work  it  is  necessary  to  remove  iron 
and  chromium  with  zinc  oxide,  and  to  oxidize  an  aliquot  part  of 
the  filtrate  with  sodium  bismuthate.  .    • 

Tungsten  steels,  which  decompose  readily  in  nitric  acid,  may 
ibe  heated  to  precipitate  the  tungstic  acid,  and,  after  filtration, 
may  be  carried  through  as  ordinary  steels.  If  solution  of  the 
;steel  is  troublesome,  it  will  be  necessary  to  use  aqua  regia  and 
.to  remove  subsequently  every  trace  of  hydrochloric  acid  by 
repeated  evaporation  with  nitric  acid. 

6.  There  must  be  no  loss  of  time  between  the  filtration  and 
the  addition  of  ferrous  sulphate,  as  permanganic  acid  gradu- 
ally decomposes  on  standing,  and  the  warmer  the  solution  is 
the  more  rapidly  does  decomposition  take  place. 

7.  The  bismuthate  method  combines  extreme  accuracy  with 
great  rapidity  and  simplicity  of  manipulation.    It  is  capable 
of  being  used,  without  loss  of  accuracy,  for  any  percentage  of 
manganese.     In  this  respect  it  has  a  distinct  advantage  over 
the  Volhard  and  Williams  methods. 

8.  A  colorimetric  method,  in  which  oxidation  to  perman- 
ganic acid  is  brought  about  by  sodium  bismuthate,  ammonium 
persulphate,  or  lead  peroxide,  is  extensively  used  for  rapid 
work  in  the  steel  mills.      The  color  of  the  permanganic  acid 
formed  is  compared  with  that  produced  in  steels  of  known 
manganese  content. 

9.  A  method,  very  similar  in  its  details  and  principle,  is  in 
extensive  use.     Instead  of  using  sodium  bismuthate  as  oxidiz- 
ing agent,  ammonium  persulphate1  is  used.    While,  in  general, 
not  so  accurate,  it  possesses  the  distinct  advantage  that  the 
excess  reagent  is  destroyed  by  heat,  thus  avoiding  one  filtration. 

10.  All  methods  involving  oxidation  of  manganese  to  per- 
manganic acid  are  not  applicable  to  cast  irons,  unless  the 
separated  carbon  is  filtered  off  before  oxidation  takes  place. 

1  Walters,  Proc.  Eng.  Soc.,  Western, Penna.,  17  (1901),  257;  Chem.  News, 
«4,  239. 


DETERMINATION  OF  PHOSPHORUS  IN  IRON  AND   STEEL      75 

DETERMINATION  OF  PHOSPHORUS  IN  IRON  AND 
STEEL 

STANDARDIZATION    OF    POTASSIUM    PERMANGANATE    AND    THE 

USE   OF   THE   JONES   REDUCTOR 

Dissolve  5  grams  of  potassium  permanganate  in  two  liters 
of  water,  and  filter  this  solution  through  some  washed  asbes- 
tos into  a  clean  bottle.  It  is  advisable  to  keep  this  solution 
in  a  cool  place  and  protected  from  the  light. 

Weigh  several  portions  of  pure  iron  wire  of  about  0.20 
gram  each  into  125  cc.  Erlenmeyer  flasks,  and  pour  into  each 
flask  30  cc.  of  water  and  10  cc.  of  concentrated  sulphuric 
acid.  Cover  with  a  watch  glass  and  heat  until  solution  is 
complete.  Add  enough  strong  permanganate  solution,  drop 
by  drop,  until  the  color  of  the  permanganate  disappears  only 
slowly.  If  an  excess  be  added,  it  is  necessary  to  reduce  by  a 
drop  of  sulphurous  acid  and  to  boil  off  this  excess  completely. 

Having  previously  gotten  ready  a  Jones  reductor,  by 
washing  with  hot  dilute  sulphuric  acid  followed  by  hot  water, 
attach  the  reductor  to  the  filter  pump,  and,  in  making  blanks 
or  in  any  determination,  proceed  exactly  as  here  described. 

Pour  100  cc.  of  hot  dilute  sulphuric  acid  (made  by  adding 
25  cc.  of  concentrated  sulphuric  acid  to  one  liter  of  water) 
into  the  funnel,  and  open  the  stopcock.  When  only  a  little 
remains  in  the  funnel  add  the  solution  to  be  reduced.  This 
solution  should  also  be  hot.  Have  ready  250  cc.  of  hot, 
dilute  sulphuric  acid,  and  when  the  solution  to  be  reduced 
has  nearly  passed  out  of  the  funnel  wash  out,  with  this  acid, 
the  beaker  containing  the  iron  or  molybdenum  solution,  as 
the  case  may  be,  and  pass  the  whole  of  the  250  cc.  of  acid 
through  the  reductor.  Follow  this  by  100  cc.  of  hot  water. 
Disconnect  the  flask  and  titrate  with  potassium  permanganate 
solution. 

Before  any  series  of  determinations,  a  blank  must  be 
made  on  the  reductor.  In  this  case  a  mixture  of  10  cc.  con- 
centrated sulphuric  acid,  5  cc.  dilute  ammonia,  and  50  cc.  of 
water  is  to  be  passed  through  the  reductor,  preceded  and 


76  QUANTITATIVE  ANALYSIS 

followed  by  the  dilute  acid  as  described  above.  The  amount 
of  potassium  permanganate  used  in  this  operation,  which 
usually  is  about  0.3  cc.,  must  be  subtracted  from  the  total 
amount  taken  in  each  determination.  Having  made  a  blank, 
this  value  will  serve  for  a  series  of  determinations,  but  a  new 
blank  should  be  made  before  each  new  series. 

METHOD 

For  steels  weigh  2  grams,  and  for  irons  weigh  a  i  gram 
sample  into  a  250  cc.  Erlenmeyer  flask.  Add  100  cc.  of 
nitric  acid  (sp.  gr.  1.13)  which  has  been  prepared  by  mixing 
one  part  of  nitric  acid  (sp.  gr.  1.42)  with  three  parts  of  water, 
and  which  has  been  tested  by  means  of  a  Westphal  balance. 
Cover  the  flask  with  a  small  watch  glass,  and  heat  the  solu- 
tion until  the  oxides  of  nitrogen  have  boiled  off.  Then  add 
10  cc.  of  potassium  permanganate  solution  (15  grams  of  the 
crystals  to  one  liter  of  water),  or,  in  the  case  of  irons  or  steels 
rich  in  iron  carbide,  enough  of  the  solution  to  produce  a  pink 
color.  Boil  until  the  pink  color  disappears  and  then  remove 
from  the  heat.  Now  add  at  intervals  crystals  of  ferrous  sul- 
phate free  from  phosphorus  until  all  of  the  manganese  dioxide 
is  dissolved.  Boil  two  minutes  longer  and  then  cool  the  flask. 
Add  cautiously  40  cc.  of  dilute  ammonia  (sp.  gr.  0.96)  and 
rotate  the  flask  until  the  precipitated  ferric  hydroxide  is  dis- 
solved. When  the  solution  has  cooled  to  about  35°  C.  add 
40  cc.  of  a  recently  filtered  solution  of  ammonium  molyb- 
date,1  close  the  flask  with  a  solid  rubber  stopper,  and  shake 
for  five  minutes.  Allow  the  precipitate  to  settle  for  a  few 
minutes,  and  filter  through  a  9  cm.  paper  which  fits  the  sides 
of  the  funnel  perfectly.  Wash  the  precipitate  several  times 
by  decantation,  and  then  completely  on  the  filter  with  a  solu- 
tion of  acid  ammonium  sulphate  (made  by  adding  25  cc.  of 

1  MOLYBDATE  SOLUTION.  —  To  ioo  grams  of  pure  molybdic  oxide  (MoO3) 
which  has  been  stirred  up  with  400  cc.  of  cold,  distilled  water  add  80  cc.  of 
concentrated  ammonia.  Filter,  and  pour  the  filtrate  slowly,  with  constant 
stirring,  into  a  solution  of  400  cc.  nitric  acid  (sp.  gr.  1.42)  in  600  cc.  of  water. 
After  the  addition  of  50  milligrams  of  microcosmic  salt,  allow  to  stand  for 
twenty-four  hours,  and  filter.  If  pure  molybdic  oxide  is  not  available,  125 
grams  of  ammonium  molybdate  may  be  substituted. 


DETERMINATION  OF  PHOSPHORUS   IN  IRON  AND   STEEL      77 

strong  sulphuric  acid  to  15  cc.  of  strong  ammonia  in  one 
liter  of  water). 

Test  the  wash  water  for  molybdenum  by  allowing  about 
ten  drops  to  run  into  a  small  specimen  tube  containing  one 
drop  of  yellow  ammonium  sulphide.  Compare  the  color  in 
this  tube  with  a  similar  tube  which  has  been  treated  with 
a  like  amount  of  acid  wash  water  and  a  drop  of  the  poly- 
sulphide.  Continue  the  washing  until  all  of  the  molybdenum 
is  removed. 

Now  pour  5  cc.  of  ammonia  (sp.  gr.  0.90)  and  20  cc.  of 
water  into  the  flask  to  dissolve  any  ammonium  phospho- 
molybdate  adhering  to  the  walls;  pass  this  solution  through 
the  filter  and  allow  the  nitrate  to  run  into  a  No.  2  beaker. 
Wash  out  the  flask  and  the  filter  with  about  75  cc.  of  water. 
To  this  solution  add  10  cc.  of  concentrated  sulphuric  acid 
and  pass  through  the  reductor  exactly  as  previously  described, 
taking  the  precaution  not  to  allow  any  air  to  enter  the  re- 
ductor. This  solution  is  preceded  and  followed  by  the  dilute 
sulphuric  acid  and  water,  just  as  in  testing  the  reductor. 
When  the  water  has  finally  been  drawn  through  with  the  ex- 
ception of  a  small  amount  in  the  funnel,  the  flask  is  detached 
and  the  reduced  solution  is  titrated  at  once  with  the  standard 
potassium  permanganate  to  a  permanent  pink  color. 

Subtract  from  the  reading  of  the  burette  the  blank  for  the 
reductor  and  calculate,  assuming  a  reduction  of  the  molyb- 
denum to  Mo24O37  by  the  zinc,  and  oxidation  to  Mo03  by 
the  permanganate. 

THE  FERRIC  ALUM  METHOD  FOR  PHOSPHORUS1 

Proceed  exactly  as  in  the  preceding  method  up  to  the 
point  of  passing  the  sulphuric  acid  solution  through  the  re- 
ductor. Instead  of  passing  the  reduced  solution  into  the 
empty  flask,  place  in  the  flask  50  cc.  of  ferric  alum  solu- 
tion,2 and  allow  the  reduced  solution  to  run  through  a  tube 

1  This  method  was  worked  out  in  the  laboratory  of  the  Penna.  R.R.  by 
Dudley  and  Pease  but  was  never  published  by  them.    It  has  been  in  successful 
use  in  this  laboratory  for  many  years. 

2  100  grams  of  FdCSC^MNHOjSO^^jO  dissolved  in  1000  cc.  H2O,  to  which 
has  been  added  25  cc.  H2SO4  (sp.  gr.  1.84).    To  this  solution  add  40  cc.  H3PO4. 


78  QUANTITATIVE  ANALYSIS 

extended  below  the  surface  of  the  liquid.  In  all  other  respects 
the  two  methods  are  identical.  The  purpose  of  the  ferric 
alum  is  to  oxidize  immediately  the  molybdenum,  which  has 
been  reduced  in  the  reductor  to  a  form  corresponding  to  the 
oxide  Mc^Os,  to  the  higher  oxide  MoO3.  The  iron  which  has 
been  reduced  in  this  reaction  is  then  titrated  with  potassium 
permanganate  solution,  and  is  a  direct  measure  of  the  molyb- 
denum reduced.  The  calculation  is  based  on  the  assumption 
that  the  molybdenum  is  reduced  to  M^Oa,  and  the  results 
should  agree  with  the  other  method  in  which  reduction  to 
M024O37  was  assumed. 

A  blank  determination  must  be  made  with  the  ferric  alum 
solution  in  the  flask,  using  the  same  amounts  of  reagents  as 
in  the  regular  procedure. 

Notes.  —  i.  The  determination  of  phosphorus  is  an  indirect 
method  dependent  upon  its  oxidation  to  phosphoric  acid  and 
precipitation  in  the  form  of  ammonium  phospho-molybdate, 
the  reduction  of  the  molybdenum  by  means  of  zinc,  and  the 
subsequent  oxidation  of  the  molybdenum  by  means  of  potas- 
sium permanganate. 

2.  The  phosphorus  exists  in  most  steels  as  a  solid  solution 
of  iron  phosphide  (FesP)  in  iron.     When  present,  as  it  may 
be  in  some  irons,  in  amounts  greater  than  1.7  per  cent  it 
separates  as  free  FesP,  and  the  iron  will  contain  the  solid 
solution,   and  also   free  iron  phosphide.     In   wrought   iron, 
and  probably  also  in  some  low  carbon  Bessemer  steels,  phos- 
phorus may  also  exist  in  the  form  of  a  phosphate. 

3.  The  preparation  of  potassium  permanganate  which  is 
to  be  used  for  a  series  of  determinations  should  be  done  with 
extreme  care.    The  crystals  of  the  salt  are  never  absolutely 
pure,  but  invariably  contain  a  small  amount  of  manganese 
dioxide.     If  this  is  not  filtered  off,  it  reacts  with  the  potas- 
sium permanganate,   giving   off   oxygen   and   forming  more 
manganese    dioxide.    The   presence    of   manganese    dioxide 
accelerates  the  decomposition,  and  when  it  is  once  formed  the 
decomposition    takes    place    rapidly.     A    solution    carefully 
prepared  will  keep  almost  indefinitely. 

4.  It  is  impossible  to  obtain  absolutely  pure  iron  wire. 
The  determination  of  the  actual  amount  of  iron  in  any  sample 


DETERMINATION  OF  PHOSPHORUS   IN  IRON  AND   STEEL      79 

may  be  done  in  either  of  two  ways:  the  impurities  in  the 
sample  or  the  actual  amount  of  iron  may  be  determined. 
The  former  method  involves  much  skill  and  experience;  the 
latter  method  is  the  simpler  and  is,  perhaps,  more  accurate. 
When  using  the  latter  method,  the  potassium  permanganate 
is  titrated  first  against  pure  electrolytic  iron,1  and  after  this 
has  been  carefully  standardized  this  solution  is  used  to  deter- 
mine the  actual  amount  of  iron  in  a  sample  of  pure  piano  wire. 
There  are  many  other  methods  for  the  standardization  of 
potassium  permanganate  solutions.  The  author  prefers  the  use 
of  sodium  oxalate  to  any  of  the  others.  This  salt  contains  no 
water  of  crystallization,  is  very  stable,  may  easily  be  prepared 
pure,  and  may  also  be  used  as  a  standard  for  alkalimetric  work.2 

5.  The  addition  of  strong  potassium  permanganate  to  the 
solution  of  iron  is  rendered  necessary  because  of  the  pres- 
ence of  a  small  amount  of  carbon.    The  decomposition  of 
iron  carbide  by  sulphuric  acid  gives  rise  to  hydrocarbons 
which  are  held  in  solution  and  which  would  affect  the  titration, 
if  not  previously  oxidized. 

6.  A  blank  on  the  reductor  is  a  necessity  on  account  of 
the  fact  that  all  zinc  contains  some  iron  which  is  given  up 
to  the  dilute  acid  passing  through  the  column  of  zinc.     The 
necessity,  therefore,  of  always  using  exactly  the  same  amounts 
of  reagents  is  apparent.    The  time  factor  is  also  apparent. 
It  is  advisable  to  measure  accurately  all  reagents,  and  in 
each  case  to  allow  approximately  the  same  amount  of  time 
for  each  reaction. 

7.  The  preparation  of  nitric  acid  of  exact  sp.  gr.  1.13  is 
important  because  in  acid  of  this  strength  the  steel  is  most 
readily  soluble,  the  phosphorus  is  oxidized  as  well  as  in  acids 
of  greater  strength,  the  silica  is  not  separated  in  the  insolu- 
ble form,  and  it  is  very  important  to  bring  down  the  yellow 
precipitate  always  in  the  same  strength  solution.     Especially 
on  account  of  this  last  reason,  the  solutions  should  never 
be  allowed  to  boil  longer  than  the  time  indicated  in  the  direc- 
tions. 

8.  Boiling  off  the  oxides  of  nitrogen  seems  to  be  necessary 

1  For  details  in  carrying  out  this  method,  consult  Treadwell-Hall's  Analyti- 
cal Chemistry,  Vol.  II. 

1  See  Spathic  Iron  Ore  Procedure,  p.  21. 


80  QUANTITATIVE  ANALYSIS 

as  these  reduce  potassium  permanganate,  which  is  to  be 
added  subsequently  to  this  operation,  and  also  on  account 
of  the  solubility  of  the  ammonium  phospho-molybdate  in 
solutions  containing  nitrous  acid. 

9.  Potassium   permanganate   is   added    to   complete    the 
oxidation  of  the  phosphorus  to  the  form  of  ortho-phosphoric 
acid  and  to  destroy  the  carbonaceous  material.     When  car- 
bide of  iron  is  boiled  with  dilute  nitric  acid  certain  organic 
compounds  are  formed,  which,  if  allowed  to  remain,  would 
hold  some  of  the  yellow  precipitate  in  solution. 

For  most  steels  10  cc.  of  permanganate  solution  is  more 
than  enough  to  oxidize  the  phosphorus  and  destroy  the  car- 
bonaceous material.  It  is  advisable,  however,  to  use  just 
this  amount  in  each  case  except  in  high  carbon  steels  or  in 
white  irons,  which  may  require  more  than  the  specified  amount 
to  complete  the  oxidation. 

10.  Instead  of  using  pure  ferrous  sulphate  for  the  removal 
of  the  manganese  dioxide,  many  other  substances,  such  as 
sulphurous  acid,  oxalic  acid,  sugar,  sodium  thiosulphate,  etc., 
have  been  recommended,  but  it  is  believed  that  for  student 
work  ferrous  sulphate  is  the  most  satisfactory. 

n.  The  addition  of  ammonia  is  simply  to  form  some 
ammonium  nitrate  in  which  the  precipitate  is  more  insoluble. 
If  by  some  oversight  too  much  nitric  acid  had  been  boiled  off 
during  the  operation,  the  ammonia  will  produce  a  permanent 
precipitate  of  ferric  hydroxide.  If  this  should  happen,  it  is 
necessary  to  add  more  nitric  acid  of  sp.  gr.  1.13. 

12.  The  composition  of  ammonium  phospho-molybdate 
depends  very  largely  upon  the  strength  of  solutions  from 
which  it  is  precipitated  and  upon  the  temperature  of  pre- 
cipitation. Produced  under  the  conditions  described  above 
it  may  be  represented  by  the  formula  (NH4)3P04,  laMoOs. 
The  ratio  of  phosphorus  to  molybdenum  is  always  P  :  i2MoOa. 
If  precipitation  takes  place  at  a  temperature  higher  than 
35°-4O°  C.,  there  is  liability  of  ammonium  arseno-molybdate 
being  precipitated  in  case  there  is  any  arsenic  in  the  sample. 

All  of  the*  molybdenum  before  passing  through  the  re- 
ductor  is  in  a  form  corresponding  to  the  oxide  Mo03,  and 
is  reduced  in  the  reductor  to  a  form  corresponding  to  the 
oxide  Mo2O3.  It  is,  however,  so  sensitive  to  the  action  of 


DETERMINATION  OF  PHOSPHORUS  IN  IRON  AND   STEEL      8 1 

oxygen  that  on  coming  in  contact  with  the  air1  in  the  flask 
it  takes  up  oxygen  from  the  air,  and  is  oxidized  to  a  form 
corresponding  to  the  oxide  MoaAtf.2  The  calculation  of 
results  must,  therefore,  be  based  upon  this  reduction. 

13.  Having    standardized    the    potassium    permanganate 
solution  against  iron,  the  conversion  of  the  iron  value  to  the 
phosphorus  value  is  very  simple,  as  is  shown  by  the  following 
equations: 

2KMnO4  o  50  =0=  loFe. 
MoaA;  +  35O  =  24MoO3. 
2P  =0=  24MoO3  =c=  yoFe. 

P  *  35Fe. 

In  the  ferric  alum  modification  advantage  is  taken  of  the 
fact  that  ferric  iron  will  oxidize  reduced  molybdenum  solu- 
tions. The  molybdenum  in  the  form  of  MoaOa  as  it  leaves 
the  reductor  reduces  a  corresponding  amount  of  iron  to  the 
ferrous  condition,  and  is  in  turn  oxidized  to  MoOs.  As  the 
ferrous  iron  is  more  stable  than  reduced  molybdenum  solu- 
tions, the  titration  is  on  the  whole  more  satisfactory. 

14.  As  the  ammonium  phospho-molybdate  has  a  strong 
tendency  to  crawl,  it  must  be  filtered  through  a  paper  which 
fits  the  funnel  perfectly.     Otherwise  it  creeps  over  the  top 
of  the  paper  and  into  the  filtrate.     It  is  necessary  to  wash 
the  edges  of  the  paper  thoroughly,  so  as  to  remove  the  last 
traces  of  iron  and  molybdenum.     If  the  iron  is  not  removed 
it  will  color  the  drop  of  yellow  ammonium  sulphide  black 
while  it  is  still  alkaline.   'The  presence  of  molybdenum  is 
shown  by  its  coloring  the  precipitated  sulphur  brown.     When 
free  from  molybdenum  the  sulphur  will  be  perfectly  white. 

15.  The  determination  of  phosphorus  in  most  of  the  alloy 
steels  involves  no  rpecial  difficulties  and  the  regular  procedure 
is  applicable  except  in  the  presence  of  large  amounts  of  tung- 
sten, vanadium,  or  chromium  when  special  methods  must  be 
used.     In  steels  containing  chromium  an  insoluble  residue, 
probably  chromium  carbide,  is  left  on  treating  with  nitric  acid. 
This  goes  into  solution  slowly  on  digestion  at  a  low  tempera- 
ture.   It  is  advisable  to  keep  the  solution  at  constant  volume 
by  the  occasional  addition  of  some  water. 

1  W.  A.  Noyes,  /.  Am.  Chem.  Soc.,  16,  553. 

2  Blair  and  Whitfield,  /.  Am.  Chem.  Soc.,  17,  747. 

3  Johnson,  /.  Ind.  and  Eng.  Chem.,  n,  113. 


82  QUANTITATIVE  ANALYSIS 

1 6.  The  best  method  for  the  gravimetric  determination  of 
phosphorus  is  the  one  which  makes  use  of  the  basic  acetate 
separation  of  the  phosphoric  acid  along  with  some  of  the  iron 
and  the  subsequent  separation,  after  the  addition  of  citric  acid 
to  hold  the  iron  hi  solution,  as  magnesium  ammonium  phos- 
phate. 

ALKALIMETRIC  METHOD  FOR  PHOSPHORUS 

HANDY  METHOD 

Proceed  exactly  as  in  the  preceding  methods  to  the  point 
of  washing  the  ammonium  phospho-molybdate  precipitate. 
Instead  of  using  acid  ammonium  sulphate  solution,  wash  with 
i  per  cent  nitric  acid  l  to  remove  iron  salts,  and  follow  with 
i  per  cent  potassium  nitrate  until  litmus  paper  shows  freedom 
from  acid.  Transfer  the  precipitate  with  the  filter  paper  to 
the  flask  in  which  precipitation  was  made,  cover  with  enough 
tenth-normal  sodium  hydroxide  solution  to  completely  dis- 
solve the  yellow  precipitate,  using  a  slight  excess,  and  then 
titrate  with  tenth-normal  nitric  acid  using  phenolphthalein 
as  indicator. 

Notes.  —  i.  The  reaction  upon  which  this  method  is  based 
is  the  following: 

2(NH4)3PO4.i2MoO3  +  46NaOH  = 

2(NH4)2HPO4  +  (NH4)2Mo04  +  23Na2MoO4  +  22H2O. 

It  is  thus  seen  that  the  ratio  of  phosphorus  to  sodium 
hydroxide  is,  P  =c=  23NaOH,  and  upon  this  basis  the  calcula- 
tions are  made. 

2.  This  method  is  extensively  used,  is  more  rapid  than  the 
methods  involving  reduction  of  the  molybdic  acid,  and  is 
accurate  for  the  average  steel. 

3.  Standardization   of   the   sodium   hydroxide   solution   is 
made  preferably  against  the  yellow  precipitate  obtained  from 
a  steel  in  which  the  phosphorus  has  been  accurately  deter- 
mined by  some  other  method.     It  is  needless  to  say  that  the 
sodium  hydroxide  solution  must  be  protected  from  carbon 
dioxide  of  the  air  and  must  be  prepared  free  from  carbonates 

1  Add  13  cc.  nitric  acid  sp.  gr.  1.42  to  i  liter  of  water. 


PETERMINATION  OF   SULPHUR   IN  STEEL  83 

by  the  introduction,  at  the  time  of  solution,  of  a  small  volume 
of  barium  hydroxide  solution. 

DETERMINATION  OF  SULPHUR  IN  STEEL 

EVOLUTION   METHOD 

Standardization  of  Iodine  and  Sodium  Thiosulphate  Solu- 
tion. —  Prepare  a  solution  of  sodium  thiosulphate  by  dissolving 
five  grams  of  the  crystallized  salt,  Na2S2O3.5H2O,  in  one  liter 
of  water.  Prepare  a  solution  of  iodine  by  dissolving  about 
2.5  grams  of  iodine  in  100  cc.  of  water  containing  5  grams  of 
pure  potassium  iodide,  and  diluting,  after  solution  is  complete, 
to  one  liter.  Standardize  these  two  solutions  against  each 
other,  using  freshly-prepared  starch  solution  as  indicator,  and 
then  standardize  the  sodium  thiosulphate  against  potassium 
permanganate  in  the  following  manner.  Draw  10  cc.  of 
standardized  potassium  permanganate  solution1  into  a  No.  5 
beaker  containing  one  gram  of  potassium  iodide  dissolved  in 
350  cc.  of  cold  distilled  water.  Add  dilute  sulphuric  acid  by 
drops,  until  the  solution  has  just  cleared  from  precipitated 
manganese  dioxide.  The  liberated  iodine  is  then  titrated  with 
sodium  thiosulphate,  freshly-prepared  starch  paste  being 
added  when  the  yellow  color  of  the  iodine  solution  has  nearly 
disappeared.  The  sharpness  of  the  end  reaction  is  much 
increased  if  the  solution  be  cooled  by  a  few  lumps  of  ice. 
Knowing  the  value  of  the  potassium  permanganate  solution, 
the  strength  of  the  sodium  thiosulphate  solution  can  be 
calculated. 

METHOD 

Construct  an  evolution  apparatus  as  follows:  Use  a  250  cc. 
round  bottom  flask  as  a  generating  flask.  Fit  into  this  a 
doubly  perforated  rubber  stopper,  through  one  hole  of  which 
is  passed  a  dropping  funnel  extending  to  near  the  bottom  of 
the  flask,  and  through  the  other  a  delivery  tube  bent  twice  at 
right  angles.  This  tube  leads  down  about  two  inches  below  the 

1  The  potassium  permanganate  may  be  standardized  as  described  on  p.  21 
by  using  sodium  oxalate  as  standard. 


84  QUANTITATIVE  ANALYSIS 

rubber  stopper  into  a  250  cc.  Erlenmeyer  flask.  From  this 
flask  have  a  short  tube  bent  at  right  angles  and  connected  by 
rubber  tubing  with  a  second  tube  bent  at  right  angles  and 
extending  to  the  bottom  of  a  second  Erlenmeyer  flask.  By  a 
similar  arrangement  connect  a  third  Erlenmeyer  flask. 

Place  10  cc.  of  a  cadmium  chloride  solution  and  50  cc.  of 
water  in  the  second  and  third  absorption  flasks,  and  50  cc.  of 
water  in  the  first  flask.  (Cadmium  chloride  solution  contains 
120  grams  CdCl2  in  1500  cc.  HsO,  and  600  cc.  NELiOH,  sp.  gr. 
0.90.) 

Weigh  into  the  generating  flask  5  grams  of  steel,  and  place 
50  cc.  of  hydrochloric  acid  (sp.  gr.  1.2)*  in  the  dropping  funnel. 

When  the  apparatus  is  shown  by  test  to  be  tight,  allow  the 
acid  to  enter  the  flask  in  small  portions,  maintaining  an  even 
and  fairly  rapid  flow  of  gas  through  the  apparatus.  When 
action  ceases  or  slackens,  warm  gently,  and  finally  boil  the 
liquid  until  steam  condenses  in  the  first  flask.  Open  the 
stopcock  of  the  dropping  funnel,  and  at  the  same  time  remove 
the  flame. 

Precipitation  usually  takes  place  only  in  the  second  flask. 
Filter  the  liquid  containing  the  cadmium  sulphide  precipi- 
tate. Wash  out  the  flask  twice  with  water  containing  a 
small  amount  of  ammonia,  then  transfer  the  filter  and  pre- 
cipitate to  a  beaker  and  pour  over  it  300  cc.  of  water.  By 
means  of  vigorous  stirring,  break  up  the  filter  paper  into 
shreds.  Rinse  out  the  guard  flask  and  the  absorption  flask 
and  tubes  with  50  cc.  of  water  to  which  5  cc.  hydrochloric 
acid  (sp.  gr.  1.20)  has  been  added.  This  should  remove  all 
sulphide.  Add  this  liquid  to  the  liquid  containing  the  filter 
paper  and  precipitate,  and  at  once  add  an  excess  of  iodine 
solution,  titrating  back  with  the  thiosulphate  solution  after  a 
few  moments.  Take  great  care  to  avoid  loss  of  hydrogen 
sulphide  before  the  addition  of  the  iodine. 

Notes.  —  i.  Sulphur  occurs  in  irons  and  steels  in  four  forms: 
(i)  iron  sulphide;  (2)  manganese  sulphide;  (3)  titanium  sul- 
phide; and  (4)  a  form,  or  forms,  not  yet  identified,  but  char- 
acterized by  certain  reactions.  Manganese  sulphide  is  the 
most  commonly  occurring  form,  and  the  sulphur  occurs  as  iron 
1  Pulsifer,  /.  Ind.  Eng.  Chem.,  10,  545. 


DETERMINATION  OF   SULPHUR  IN  STEEL  85 

sulphide  only  when  there  is  insufficient  manganese  present  to 
combine  with  it.  The  occurrence  of  titanium  sulphide  is  rare, 
although  it  is  occasionally  found  in  irons  made  from  ores 
carrying  small  amounts  of  titanium.  The  unidentified  form 
does  not  respond  to  the  reactions  of  the  other  three  forms  and 
there  is  some  evidence,  although  not  by  any  means  conclusive, 
that  there  may  be  a  combination  with  carbon,  or  silicon,  or 
both. 

2.  The  effect  of  sulphur,  when  existing  as  iron  sulphide,  is 
to  make  the  metal  "red-short,"  i.e.,  brittle  at  the  forging 
temperatures.     This  effect  is  overcome  by  the  addition  of 
manganese,   which  converts  iron   sulphide  into  manganese 
sulphide.     The  red-shortness  is  destroyed,  but  in  some  cases 
the  sulphide  of  manganese  is  rolled  out  into  filaments,  and 
these,  being  brittle  and  weakly  cemented  to  the  steel  surround- 
ing them,  become  points  of  weakness. 

The  most  important  effect  of  sulphur  is  its  influence  upon 
the  forms  of  carbon.1  In  castings  where  form  is  more  of  a 
factor  than  strength,  high  sulphur  irons  may  be  used  so  as  to 
get  a  very  fluid  metal.  In  these  castings  the  carbon  is  always 
in  the  combined  form,  and  the  iron  is  white  or  gray. 

3.  The  evolution  method  for  sulphur  hi  steel  is  based  upon 
the  assumption  that  all  of  the  sulphur  will  be  evolved  as 
hydrogen  sulphide,  which  may  be  determined  by  titration 
with  iodine.    The  reactions  involved  are  the  following: 

1.  MnS  +  2HC1  =  MnCl2  +  H2S. 

2.  H2S  +  2l  =   2HI  +  S. 

The  standardization  of  the  iodine  and  sodium  thiosulphate 
solutions  is  based  upon  these  reactions: 

1.  2KMnO4  +  toKI  +  8H2SO4  =  6K2S04  +  2MnSO4  + 

8H20  +  5I2. 

2.  2l  +  2Na2S2O3  =  2NaI 


This  method  of  standardization  is  most  accurate  and  con- 
venient if  one  has  ready  a  standard  potassium  permanganate 
solution.  Other  methods  of  standardization,  such  as  the 
titration  of  iodine  against  pure  arsenious  acid,  the  titration  of 
sodium  thiosulphate  against  pure  iodine,  or  the  use  of  a  steel  of 

1  See  note,  p.  62. 


86  QUANTITATIVE  ANALYSIS 

known  sulphur  content,  may  be  used,  but  the  time  involved 
is  usually  greater,  and  no  greater  accuracy  is  secured. 

4.  Instead  of  titrating  hydrogen  sulphide  against  iodine, 
the  hydrogen  sulphide  may  be  passed  directly  into  some 
oxidizing  agent,  such  as  ammoniacal  hydrogen  peroxide,  alka- 
line potassium  permanganate,  or  hydrochloric  acid  saturated 
with  bromine.     The  sulphuric  acid  formed  may  then  be  pre- 
cipitated and  weighed  as  barium  sulphate.     Indirect  oxidation 
may  also  be  used  by  absorbing  in  an  alkaline  lead  salt,  or 
ammoniacal  zinc  or  cadmium  salts  and  subsequently  oxidizing 
the  sulphides  formed. 

5.  The  assumption  that  all  of  the  sulphur  of  an  iron  or  steel 
is  evolved  as  hydrogen  sulphide  is  not  strictly  correct,  in  fact 
some,  steels  and  irons  yield  none  of  their  sulphur  as  hydrogen 
sulphide.     Part  of  it  may  be  evolved  as  a  sulphur  ether 
(CHs^S,  or  some  analogous  compound,  and  part  of  it  may 
remain  as  a  residue  unacted  upon  by  hydrochloric  acid.1 

Phillips2  was  the  first  to  point  out  that  certain  irons  gave 
low  results,  due  to  loss  of  sulphur  hi  combination  with  carbon 
and  hydrogen.  He  showed  that  oily  drops  containing  sulphur 
were  formed  and  that  sulphur  in  this  form  was  not  oxidized 
by  the  usual  oxidizing,  absorbing  agents,  nor  did  this  form 
react  with  lead,  zinc  or  cadmium  salts  to  form  sulphides.  To 
overcome  this  difficulty,  he  proposed  passing  the  evolved 
gases  through  a  heated  tube  before  passing  into  the  absorbing 
agent.  In  this  way  the  organic  sulphide  was  broken  down  in 
the  presence  of  hydrogen  to  hydrogen  sulphide. 

Various  workers  have  recommended  annealing  the  metal 
before  placing  in  the  evolution  flask,  and  have  obtained 
improved  results.  Elliot3  recommends  annealing  in  a  closed 
muffle  a  five-gram  sample  mixed  with  0.25  gram  dry  potas- 
sium ferrocyanide  and  wrapped  in  one  n  cm.  filter  paper. 
The  best  temperature  for  annealing  is  between  750°  and  850°  C. 
and  the  time  twenty  minutes.  Steels  so  treated  give  satis- 
factory results  by  the  evolution  process. 

Because  of  the  difficulties  mentioned  the  evolution  process 
should  never  be  used  where  an  absolute  value  is  wanted.  In 

1  Blair,  J.  Am.  Chem.  Soc.,  19,  114. 

2  Phillips,  /.  Am.  Chem.  Soc.,  17,  891. 

3  J.  Iron  and  Steel  Inst.,  ign,  No.  i,  4.12. 


DETERMINATION  OF   SULPHUR   IN   CAST   IRON  87 

a  majority  of  cases  it  will  yield  fairly  accurate  results,  and  by 
annealing  the  sample,  improved  results  are  obtained,  but 
where  there  is  any  question  of  controversy  the  Bamber  method 
should  be  employed. 

6.  Iodine  and  sodium  thiosulphate  solutions  are  subject 
to  change,  and  their  values  should  be  verified  frequently. 
The  titration  of  iodine  by  sodium  thiosulphate  in  weak  acid 
solution  gives  accurate  results,  but  the  acid  must  be  weak  and 
the  solution  cool. 

7.  Wiborgh 1  has  devised  a  colorimetric  process  for  sulphur 
in  steel,  based  upon  the  depth  of  color  attained  by  a  cloth 
treated  with  a  cadmium  salt.    The  evolved  gases  are  passed 
through  the  cloth  placed  over  the  mouth  of  the  generating 
vessel,  and  this  cloth  is  compared  either  with  a  standard,  or  a 
steel  of  known  sulphur  content. 

DETERMINATION    OF    SULPHUR    IN    CAST    IRON 

BAMBER  METHOD2 

Weigh  five  grams  of  borings  into  a  250  cc.  porcelain  casserole, 
and  treat  with  40  cc.  of  concentrated  nitric  acid.  The  reaction 
may  be  violent,  and  it  is  wise  to  have  ready  a  beaker  of  cold 
water  into  which  to  dip  the  casserole  in  order  to  slow  down  the 
reaction.  Evaporate  to  about  one-half  the  volume  and  then 
add  5  grams  of  sodium  carbonate.  Transfer  to  a  platinum 
dish,  and  evaporate  to  dryness,  stirring  the  pasty  mass  from 
time  to  time.  Ignite  over  an  alcohol  flame  until  the  oxides  of 
nitrogen  are  completely  driven  off.  After  cooling,  treat  with 
20  cc.  of  a  five  per  cent  solution  of  sodium  carbonate  and 
bring  to  boiling.  Allow  to  settle,  and  decant  through  a  filter 
into  a  No.  4  beaker.  Repeat  this  process  several  times. 
Acidulate  the  filtrate  with  hydrochloric  acid,  evaporate  to 
dryness,  re-dissolve  in  water  with  a  few  drops  of  hydro- 
chloric acid,  filter  if  necessary,  and  precipitate  in  the  boiling 
solution  with  barium  chloride.  Allow  to  stand  until  the 
precipitate  has  settled,  filter,  wash,  and  ignite  as  in  the  analysis 
of  pyrite. 

1  Stahl  und  Eisen,  6,  240. 

*  J.  Iron  and  Steel  Inst.,  1894,  No.  i,  319. 


88  QUANTITATIVE  ANALYSIS 

Notes.  —  i.  Some  steels  and  irons  will  not  yield  all  of  their 
sulphur  in  the  form  of  sulphuric  acid  when  treated  with  con- 
centrated nitric  acid  or  with  aqua  regia,  nor  as  hydrogen 
sulphide  on  treatment  with  hydrochloric  acid.  Furthermore, 
the  precipitation  of  barium  sulphate  in  the  presence  of  iron 
salts  is  always  an  uncertain  and  inaccurate  process.  In  order 
to  overcome  these  difficulties  and  to  obtain  all  of  the  sulphur, 
a  fusion  process  must  be  used.  The  direct  fusion  of  the  steel 
is  a  very  slow  and  uncertain  process.  Bamber  proposed  to 
overcome  this  by  a  combination  solution  and  fusion  process. 
In  this  method  partial  oxidation  is  accomplished  by  nitric 
acid,  and  complete  oxidation  by  fusion  with  sodium  nitrate 
and  by  the  decomposition  of  ferric  nitrate  into  oxide  of  iron 
and  the  strongly  oxidizing  oxides  of  nitrogen.  Bamber's 
method  has  the  distinct  advantage  over  other  methods  in  that 
all  of  the  sulphur,  in  whatever  form  present,  is  obtained,  and, 
further,  that  precipitation  of  the  barium  sulphate  is  made  in 
the  absence  of  iron  and  under  well-controlled  conditions. 

2.  Concentrated  nitric  acid  frequently  renders  steel  or  iron 
passive,  and  solution  takes  place  only  with  difficulty.    In 
order  to  hasten  solution,  it  is  advisable  to  add,  from  time  to 
time,  one  or  two  drops  of  concentrated  hydrochloric  acid. 
The  hydrochloric  acid  must  never  be  present  in  excess,  as  loss 
of  sulphur  as  sulphur  dioxide  will  result. 

3.  Evaporation  to  dryness  of  the  ferric  nitrate  solution  is 
a  tedious  operation.    To  prevent  spattering  and  caking  of 
the  surface,  the  mass  must  be  stirred  frequently. 

An  alcohol  flame  is  not  absolutely  necessary  for  the  ignition, 
but  is  desirable.  By  placing  the  dish  in  an  opening  in  an 
asbestos  board,  gas  may  be  used  for  the  ignition,  but  the  board 
must  be  large  enough  to  deflect  the  products  of  combustion 
of  the  gas.  The  platinum  dish  is  always  attacked  to  an 
appreciable  extent  by  the  ignition,  and  the  process  has,  there- 
fore, the  disadvantage  of  the  wear  on  the  platinum. 

4.  Sodium  carbonate  is  used  to  wash  out  the  sulphates,  so 
as  to  decompose  any  basic  salts  which  may  be  present. 

5.  Pulsifer1  has  recommended  the  use  of  chloric  acid  as 
solvent  and  oxidizing  agent  for  the  determination  of  sulphur 
in  steel,  and  claims  excellent  results  for  the  method.    He  says 

1  /.  Ind.  Eng.  Ghent.,  8,  1115. 


DETERMINATION  OF   SILICON  IN  CAST  IRON  89 

that  the  Bamber  method  is  liable  to  give  slightly  high  results 
on  account  of  the  tendency  to  absorb  sulphur  from  outside 
sources,  and  the  nitric  acid  oxidation  method  gives  low  results 
because  of  the  solubility  of  barium  sulphate  in  ferric  chloride 
solution. 

An  excellent  bibliography  of  the  determination  of  sulphur 
in  iron  and  steel  is  given  in  this  paper. 

DETERMINATION   OF   SILICON   IN   CAST   IRON 

METHOD   OF  DROWN 

For  the  determination  of  silicon  in  cast  iron,  weigh  a  one- 
gram  sample;  for  wrought  iron  and  steel,  weigh  a  three-gram 
sample.  Treat  the  borings  in  a  casserole  with  a  mixture  of 
15  cc.  of  water  and  15  cc.  of  nitric  acid  (sp.  gr.  1.42).  As  soon 
as  the  reaction  has  ceased,  add  25  cc.  of  sulphuric  acid,  made  by 
mixing  equal  parts  of  the  concentrated  acid  and  water. 
Evaporate  to  dryness  on  the  steam  table  and  then  heat  over 
a  free  flame  in  a  well  ventilated  hood  until  the  sulphuric  acid 
fumes  strongly.  Allow  to  cool  and  then  add  150  cc.  of  water 
and  5  cc.  of  dilute  hydrochloric  acid.  Heat  until  the  solution 
of  the  ferric  sulphate  is  complete  and  filter  by  suction  at  once. 
Wash  with  dilute  hydrochloric  acid  (one  part  acid  sp.  gr.  1.12 
to  three  parts  of  water)  until  the  filter  paper  is  free  from 
iron  stain,  and  with  hot  water  to  remove  the  hydrochloric 
acid.  Place  the  filter  and  silica  in  a  platinum  crucible,  char 
the  paper  slowly  and  ignite  with  the  crucible  on  its  side  and 
the  lid  partially  covering  the  mouth. 

The  graphite  from  cast  iron  burns  off  very  slowly  and  con- 
sequently the  crucible  should  be  so  placed  as  to  have  as  much 
air  as  possible.  When  the  ignition  is  complete,  cool  in  a 
desiccator,  weigh,  and  treat  the  contents  of  the  crucible  with 
hydrofluoric  and  sulphuric  acids  exactly  as  in  silicate  analysis. 
Weigh  again.  The  difference  in  weight  is  silica. 

Notes.  —  i.  Silicon  exists  in  cast  irons  and  steels  for  the 
most  part  in  the  form  of  a  solid  solution  of  the  compound 
in  iron.    In  wrought  iron  and  some  low  carbon  steels, 


90  QUANTITATIVE   ANALYSIS 

part  of  it  may  also  exist  in  the  oxidized  form  as  silicate  of  iron 
or  silicate  of  manganese.  A  silicate  of  manganese  having  the 
composition  2MnO.3SiC>2  has  been  isolated  from  steel  by 
Stead.1 

In  ferro-silicon,  the  silicon  may  exist  as  a  solid  solution  of 
the  compound  Fe2Si  hi  iron;  as  the  compounds  Fe2Si  or  FeSi, 
or  mixtures  of  these  two;  and  as  mixtures  of  FeSi  with  silicon, 
the  relative  proportions  of  each  being  dependent  upon  the 
percentage  of  silicon  present. 

2.  The  influence  of  silicon  hi  small  amounts  upon  steel  has 
not  been  well  established,  except  hi  its  effect  upon  the  shrink- 
age hi  cast  steels.     In  such  steels,  the  excessive  shrinkage  can 
be  counteracted  by  the  introduction  of  silicon,  the  amount 
remaining  hi  the  metal  being  about  0.30  per  cent.    It  also 
diminishes  blow  holes  hi  castings. 

In  cast  irons,  the  silicon  influences  the  form  of  carbon  very 
markedly.  With  increasing  percentages  of  silicon,  there  is  a 
corresponding  increase  hi  the  amount  of  carbon  in  the  form  of 
graphite.  While  cast  irons  are  graded  upon  the  appearance 
of  graphite  hi  the  fractured  surface,  it  is  the  silicon  which 
influences  the  character  of  this  appearance.  The  appearance 
of  the  fracture  is  also  undoubtedly  influenced  by  temperature 
and  time  of  cooling.2 

3.  Nitric  acid  is  used  hi  preference  to  hydrochloric  or  sul- 
phuric acids  for  solution  because  it  will  decompose  any  titanium 
carbide  which  might  be  present  hi  titaniferous  pig  irons.     In 
the  other  acids  it  is  insoluble  and  would  be  left  in  the  siliceous 
residue. 

4.  Evaporation  to  free  fuming  of  the  sulphuric  acid  is 
necessary,  otherwise  there  is  incomplete  dehydration  of  the 
silica.     More  complete  dehydration  takes  place  hi  sulphuric 
acid  than  in  hydrochloric  acid  solutions. 

Nitric  acid,  when  being  freely  removed,  will  fume  hi  moist 
air  and  this  must  not  be  mistaken  for  sulphuric  acid. 

During  the  evaporation,  the  ferric  sulphate  is  liable  to 
spatter.  It  is,  therefore,  necessary  to  have  a  watch  glass  of 
sufficient  size  to  cover  the  casserole  and  to  rotate  the  casserole 
during  the  final  heating. 

1  Stead,  Iron  and  Steel  Magazine,  9,  105. 
»  Adamson,  /.  I.  &  S.  Inst.  1911,  No.  2,  86. 


DETERMINATION  OF   COPPER  IN   STEEL  91 

5.  The  filtration  of  the  silica  must  take  place  soon  after 
the  solution  of  the  ferric  sulphate  is  complete  on  account  of 
the  tendency  of  the  silica  to  go  back  into  solution.     Losses 
amounting  to  fully  half  of  the  total  silica  may  occur  on  allow- 
ing the  solution  to  stand  over  night. 

6.  In  cast  irons,  the  burning  of  the  graphitic  residue  is  a 
tedious  operation  and  cannot  be  helped  much  by  the  use  of  the 
blast  lamp.     It  is  advisable  to  start  this  ignition,  and,  in  the 
meantime,  continue  other  work  until  the  silica  becomes  white. 

7.  In   some  ferro-silicons,   solution  in  acids   takes  place 
extremely  slowly.     In  high  silicon  products  such  as  ferro- 
silicon,  "Duriron,"  etc.,  it  is,  therefore,  more  advantageous 
to  fuse  at  once  with  sodium  carbonate  or  with  a  mixture  of 
sodium  carbonate  and  sodium  peroxide  and  to  treat  the  fusion 
as  in  the  analysis  of  feldspar. 


DETERMINATION  OF  COPPER  IN  STEEL 

Dissolve  5  grams  of  steel  in  75  cc.  of  nitric  acid  (sp.  gr.  1.20) 
by  gently  heating  in  a  covered  250  cc.  porcelain  casserole. 
When  solution  is  complete,  add  25  cc.  of  dilute  sulphuric  acid 
(i  :  i)  and  evaporate  until  the  acid  fumes  freely.  Dissolve 
by  heating  with  50  cc.  of  water  and  10  cc.  of  dilute  sulphuric 
acid,  filter  into  a  500  cc.  Erlenmeyer  flask  and  wash  the  silica 
with  hot  water.  Dilute  the  filtrate  to  300  cc.,  add  25  cc.  of 
concentrated  freshly  prepared  ammonium  bisulphite  solution, 
and  heat  to  boiling.  When  the  iron  is  completely  reduced, 
add  30  cc.  of  a  20  per  cent  solution  of  sodium  thiosulphate, 
and  continue  the  boiling  until  the  sulphide  of  copper  is  coagu- 
lated. Filter,  wash  with  hot  water,  and  ignite  in  a  porcelain 
crucible.  Dissolve  in  a  small  amount  of  concentrated  nitric 
acid,  nearly  neutralize  with  ammonia,  transfer  to  a  platinum 
crucible  and  electrolyze,  making  the  crucible  the  cathode, 
Wash  the  crucible  with  water  after  all  of  the  copper  is  de- 
posited, then  with  alcohol,  dry  and  weigh. 

Notes.  —  i.  Copper  may  be  found  in  small  amounts  in 
nearly  all  steels,  and  is  added  to  sheet  steel  in  amounts,  usually 
under  0.25  per  cent,  in  order  to  retard  corrosion.  Steels  thus 


92  QUANTITATIVE   ANALYSIS 

treated  resist  ordinary  corrosive  action  of  the  weather  much 
better  than  ordinary  steels. 

The  effect  of  copper  upon  the  physical  properties  has  not 
been  definitely  determined.  In  high  carbon  steels  there  is 
a  tendency  for  the  copper  not  to  alloy  with  the  iron. 

In  high-speed  tool  steels  copper  is  detrimental. 

2.  The  principle  involved  in  this  method  is  dependent  upon 
the  precipitation  of  the  copper  as  sulphide  in  a  solution  in 
which  the  iron  has  been  reduced,  its  conversion  into  nitrate 
and  the  deposition  of  metallic  copper  by  electrolysis. 

3.  Instead  of  depositing  the  copper  as  metal,  the  sulphide 
may  be  ignited  and  weighed  as  oxide,  but  it  is  always  con- 
taminated with  iron  and  hence  the  results  are  less  accurate. 

The  solut'.on  obtained  in  the  evolution  method  for  sulphur, 
or  the  filtrate  from  the  silicon  determination  may  be  used 
for  the  precipitation  of  copper. 

4.  The  purpose  of  the  ammonium  bisulphite  is  to  reduce  the 
iron  to  the  ferrous  condition.     Sodium  thiosulphate  could  be 
used,  but  it  would  involve  the  separation  of  a  large  amount  of 
free  sulphur. 

5.  The  reaction  between  copper  salts  and  sodium  thiosul- 
phate is  complicated.     The  principal  reaction  is  the  reduction 
of  the  cupric  ion  to  cuprous  ion  and  at  the  same  time  oxi- 
dation of  the  S-A"  ion  to  S4O6",  SO3"  and  SO4"  ions.    There 
are  also  formed  complex  cupro- thiosulphate  ions   (CuSaOs)', 
which  decompose  in  boiling  solution  with  formation  of  Cu2S. 

6.  The  volumetric  method  may  be  used  for  the  determina- 
tion of  copper.     In  case  it  is  desired  to  do  this,  proceed  exactly 
as  in  the  Low  method  after  having  dissolved  the  copper  sul- 
phide in  nitric  acid. 

DETERMINATION  OF  NICKEL  IN  STEEL 

METHOD    OF    BRUNCK1 

Weigh  0.5-0.6  gram  of  steel  into  a  No.  4  beaker,  and  dis- 
solve in  20  cc.  of  hydrochloric  acid,  sp.  gr.  1.12.  To  the 
solution  add  about  i  cc.  concentrated  nitric  acid  and  boil  to 
oxidize  all  of  the  iron.  The  solution  is  filtered  if  silica  has 
separated,  or  in  the  case  of  a  high  silicon  steel,  it  should  be 
1  Z.  angew.  Chem.  (1907),  1844. 


DETERMINATION  OF  NICKEL  IN  STEEL  93 

evaporated  to  dryness  to  remove  silica.  To  the  solution  is 
added  2  to  3  grams  of  tartaric  acid,  and  it  is  then  diluted  with 
water  to  about  300  cc.  Add  ammonia  in  slight  excess  and  if 
no  ferric  hydroxide  separates,  make  slightly  acid  with  hydro- 
chloric acid,  and  heat  to  near  boiling.  Add  20  cc.  of  a  i  per 
cent  alcoholic  solution  of  dimethylglyoxime,  and  ammonia, 
drop  by  drop,  till  present  in  slight  excess.  Allow  to  stand 
for  one  hour,  collect  the  deep-red  precipitate  on  a  Gooch 
crucible,  wash  with  hot  water,  dry  at  110°  for  45  minutes, 
and  weigh  as  NKC^^CfeV 

Notes.  —  Nickel  forms  with  iron  a  series  of  homogeneous 
solid  solutions  for  all  concentrations.  Its  addition  to  steel 
raises  the  strength  and  particularly  the  elastic  limit  without 
corresponding  loss  in  ductility.  (See  Carbon.)  By  the  use 
of  nickel  steel  it  is  possible  to  get  a  greater  strength  with  smaller 
cross  section  than  with  a  carbon  steel.  For  this  reason  it  is 
used  extensively  in  manufacturing  parts  where  the  total  weight 
is  an  important  consideration,  such  as  in  bicycle  and  automo- 
bile parts. 

The  most  useful  nickel  steels  are  those  which  contain  2-3.75 
per  cent  nickel,  and  0.1-0.65  Per  cent  carbon.  For  marine 
boiler  tubes,  condensers,  etc.,  low  carbon,  25-30  per  cent 
nickel  steels  are  used,  which  have  the  advantage  of  being  more 
non-corrosive  than  carbon  steels,  and  relatively  very  much 
lighter  in  weight. 

Nickel  affects  the  carbon  condition  to  a  very  marked  extent. 
Ordinary  nickel  steels  containing  3.5  per  cent  of  nickel,  and 
carbon  up  to  0.80  per  cent  are  pearlitic,  but  with  increasing 
percentages  of  carbon  are  either  martensitic  or  austenitic. 
With  lower  carbon  these  same  changes  are  produced  with 
increase  of  nickel.  For  example,  a  0.2  per  cent  carbon  steel 
is  pearlitic  up  to  8  per  cent  nickel;  martensitic  with  12-20 
per  cent  nickel;  and  austenitic  above  25  per  cent  nickel. 

2.  The  principle  involved  in  the  separation  of  nickel  from 
iron  is  based  upon  the  insolubility  of  nickel  dimethylglyoxime1 
in  slightly  ammoniacal  solution,  the  ferric  oxide  being  held  in 
solution  in  the  form  of  a  complex  ion  in  combination  with  tar- 

1  Tschugaeff,  Berichte,  38,  2520;  Brunck,  Stahl  und  Risen,  28,  331;  Brunck, 
Z.  angew.  Chem.  (1907),  1844;  Prettner,  Chem.  Ztg.,  33,  396. 


94  QUANTITATIVE   ANALYSIS 

taric  acid.  The  method  separates  nickel  from  cobalt,  iron, 
chromium,  manganese,  copper,  tungsten,  and  vanadium.  If 
much  manganese  is  present,  the  separation  should  be  made  in 
acetic  acid  solution. 

3.  Another  principle  frequently  used  for  the  separation  of 
iron  from  nickel  is  based  upon  the  solubility  in  ether  of  ferric 
chloride1  in  hydrochloric  acid  solution,  sp.  gr.  i.n.     By  this 
method  most  of  the  ferric  chloride  can  be  removed  not  only 
from  nickel,  but  from  cobalt,  manganese,  chromium,  aluminum 
and  titanium,  thus  giving  a  simple  means  of  removing  most  of 
the  iron  from  these  elements.     This  principle  has  also  been 
used  to  advantage  for  the  removal  of  iron  in  sulphur  deter- 
minations, the  ferric  chloride  being  soluble,  and  the  sulphate 
insoluble.    The  removal  of  the  small  amount  of  iron  left  in 
solution  after  the  ether  separation  is  a  comparatively  simple 
operation.     The  separation  from  nickel  may  be  made  by  means 
of  ammonia  and  ammonium  chloride,  or  by  the  basic  acetate 
process. 

4.  In  some  methods  for  the  determination  of  nickel,  it  is 
necessary  to  remove  copper  first.     This  is  so  when  iron  is 
removed  by  means  of  ammonia  and  ammonium  chloride,  or  by 
ether.     The  nickel  is  subsequently  precipitated  as  sulphide, 
ignited  and  weighed  as  oxide.    When  nickel  is  determined 
volumetrically  by  means  of  potassium  cyanide,  it  is  also 
necessary  to  remove  copper  first. 

5.  Nickel  may  be  determined  volumetrically  without  the 
removal  of  copper  by  making  use  of  the  reaction  between 
potassium    cyanide    and    the    nickel    ammonia    complex, 
Ni(NH3)6++,  as  expressed  by  the  equation: 

(NO3)2  +  4KCN  =  K2[Ni(CN)4]  +  6NHa  +  2KNO3. 


The  nickel  glyoxime  is  separated  by  filtration  on  an  asbestos 
filter,  formed  on  a  perforated  porcelain  plate  in  an  ordinary 
funnel.  The  precipitate  is  washed  with  water  and  then 
transferred  in  the  funnel  to  a  dean  eight-ounce  suction  flask. 
Dissolve  the  precipitate  on  the  filter  with  10  to  20  cc.  of  hot 
concentrated  nitric  acid,  added  drop  by  drop,  and  wash  four 
or  five  tunes  with  water,  the  process  being  conducted  with 
suction.  The  nickel  solution  is  then  poured  into  the  beaker 

1  Rothe,  Mittheilungen  Konig.  Tech.  Versuchs.  zu  Berlin,  1892. 


DETERMINATION  OF  CHROMIUM  IN  STEEL  95 

in  which  the  precipitation  was  made,  several  crystals  of 
ammonium  persulphate  added  and  the  solution  is  boiled  for 
3  to  5  minutes.  The  solution  should  be  perfectly  clear  at 
this  point,  but  if  any  turbidity  persists,  it  should  be  filtered. 
Ice  may  be  added  to  cool  the  solution,  which  is  then  made 
slightly,  but  distinctly  ammoniacal  and  10  cc.  each  of  silver 
nitrate  and  potassium  iodide  solutions  are  added  as  indicator, 
and  titration  is  conducted  with  a  standardized  cyanide  solution. 

Silver  nitrate  —  0.5  gram  AgNO3  in  1000  cc.  water. 

Potassium  iodide  —  20  grams  KI  in  1000  cc.  water. 

Cyanide  —  approximately  4.57  grams  of  KCN  in  1000  cc, 
water. 

DETERMINATION  OF   CHROMIUM   IN  STEEL 

METHOD   OF   BARBA1 

Weigh  1.5-2  grams  of  steel  into  a  300  cc.  Erlenmeyer  flask, 
and  dissolve  in  20  cc.  sulphuric  acid  (1:5).  Heat  to  boiling, 
and  add  drop  by  drop  concentrated  nitric  acid  until  all  the  iron 
is  completely  oxidized.  If  a  residue  remains  it  should  be 
filtered  off,  ignited  and  fused  with  a  small  amount  of  sodium 
carbonate  and  potassium  nitrate.  The  fusion  should  then  be 
taken  up  in  a  small  amount  of  dilute  sulphuric  acid  and  added 
to  the  main  solution.  Boil  off  the  oxides  of  nitrogen,  dilute 
with  boiling  water  to  150  cc.  and  add  5  cc.  saturated  potassium 
permanganate  solution  or  more  if  necessary  to  produce  a 
permanent  pink  color.  Boil  15  to  20  minutes,  and  if  after  this 
time  the  color  of  the  permanganate  persists,  add  25  cc.  strong 
ammonia.  Digest  at  a  low  heat  with  occasional  stirring  for 
half  an  hour  or  until  the  excess  permanganate  is  destroyed. 
Then  add  cautiously  20  cc.  dilute  sulphuric  acid  (i  :  i),  and 
heat  for  i  to  2  minutes  to  boiling.  Cool  the  solution  to  room 
temperature,  transfer  to  a  250  cc.  graduated  flask  and  dilute 
to  the  mark.  Mix  thoroughly  by  pouring  back  and  forth  into 
a  dry  beaker.  Allow  the  precipitate  to  settle,  filter  through 
a  4-inch  Swedish  filter,  rejecting  the  first  few  cc. ;  measure  off 
200  cc.  of  the  clear  filtrate,  add  an  excess  of  standard  ferrous 
1  Iron  Age,  52,  153. 


96  QUANTITATIVE  ANALYSIS 

sulphate,  and  determine  the  excess  by  means  of  standard 
potassium  permanganate. 

Notes.  —  i.  Chromium  as  a  constituent  of  steel  has  the 
effect  of  increasing  the  strength  and  the  hardness,  and  chrome 
steels  are  always  finer  grained  than  plain  carbon  steels.  They 
are  always  used  in  the  heat  treated  condition  and  the  properties 
are  susceptible  of  great  modifications  by  heat  treatment. 
Where  extreme  hardness  is  desirable,  chrome  steels  are  used 
and  for  dies,  rolls  for  cold  rolling  metals,  balls,  and  roller  bear- 
ings give  excellent  service.  The  Aci  point  is  slightly  raised, 
and,  therefore,  chrome  steels  must  be  hardened  at  a  higher 
temperature  than  plain  carbon  steels. 

Chrome-nickel  steels  have  many  desirable  properties  in  the 
heat-treated  condition  and  are  used  extensively,  particularly 
in  automobile  parts.  For  such  uses  the  chromium  may  vary 
from  0.50  per  cent  to  1.50  per  cent  and  the  nickel  from  1.25 
per  cent  to  3.50  per  cent. 

These  steels  are  also  used  for  armor  plate  and  projectiles. 

Mayari  steel  is  made  from  an  ore  mined  in  Mayari,  Cuba, 
which  contains  chromium  and  nickel.  This  steel  is  used  for 
rails  and  automobile  parts. 

High  Speed  tool  steels  contain  chromium  and  tungsten  with 
about  2.50  to  5.00  per  cent  of  chromium  and  about  18.00  per 
cent  of  tungsten.  They  may  be  free  from  vanadium,  but 
most  of  those  on  the  market  now  carry  small  amounts  (0.50- 
2.00  per  cent)  of  this  element. 

2.  The  principles  involved  in  this  method  are  based  on  the 
oxidation  of  chromium  to  chromic  acid  in  dilute  sulphuric 
acid  solution  by  means  of  concentrated  potassium  perman- 
ganate, the  reduction  of  the  chromic  acid  by  means  of  ferrous 
sulphate,  and  the  estimation  of  the  excess  ferrous  sulphate  by 
means  of  standard  potassium  permanganate  solution.  The 
reactions  involved  in  the  calculation  of  results  are  as  follows: 

i.   H2Cr207  +  6FeS04  +  6H2SO4  =  3Fe2(SO4)3  +  Cr2(SO4)3 


2.   2KMn04  +  ioFeSO4  +  8H2S04  =  5Fe2(SO4)3  +  K2S04 
2MnS04 


DETERMINATION  OF  CHROMIUM  IN  STEEL  97 

3.  Chromium  and  iron  may  be  separated  by  means  of  ether 
in  the  same  manner  as  nickel  and  iron.     The  solution  contain- 
ing the  chromium  ions  may  be  oxidized  to  chromate  ion,  and 
then  determined  either  by  gravimetric  or  volumetric  means. 

4.  The  iron  is  oxidized  with  nitric  acid  in  order  to  avoid 
the  use  of  a  larger  amount  of  potassium  permanganate  and  the 
subsequent  formation  of  large  quantities  of  manganese  salts 
and  of  manganese  dioxide. 

5.  The  value  of  the  ferrous  sulphate  solution  in  terms  of 
potassium  permanganate  should  be  determined  each  day  before 
using. 

6.  Sodium  bismuthate  may  be  used  to  oxidize  chromium 
from  the  trivalent  to  the  hexavalent  condition  if  added  to  the 
hot  solution.     The  chromic  acid  formed  is  not  decomposed 
in  the  boiling  solution,  and  it  may  be  separated  by  nitration 
from  excess  sodium  bismuthate  and  from  precipitated  manga- 
nese dioxide. 

DETERMINATION    OF    CHROMIUM    IN    CHROME- 
VANADIUM   STEEL 

METHOD    OF   CAIN1 

Weigh  1-2  grams  of  steel  into  a  300-00.  Erlenmeyer  flask, 
and  dissolve  in  concentrated  hydrochloric  acid,  using  10  cc.  of 
acid  per  gram.  When  solution  is  complete  dilute  to  150  cc. 
with  hot  water,  and  add  saturated  sodium  carbonate  solution 
until  nearly  neutralized.  Add  barium  carbonate  emulsion  in 
slight  excess,  boil  vigorously  10-15  minutes,  with  small  addi- 
tions of  emulsion  every  two  or  three  minutes.  Not  more  than 
1-2  grams  excess  of  barium  carbonate  should  be  added,  and 
care  should  be  exercised  to  keep  the  flask  covered  as  much  as 
possible  while  adding  it. 

Remove  the  flask  from  the  heat,  allow  the  precipitate  to 
settle  and  filter  on  an  1 1  cm.  filter  paper,  washing  twice  with 
hot  water.  Ignite  the  precipitate  in  a  platinum  crucible, 
mix  with  two  grams  of  sodium  carbonate  and  0.25  gram  potas- 
sium nitrate.  Fuse  for  20  minutes. 

Extract  the  melt  by  placing  the  crucible  on  the  bottom  of  a 
small  beaker  and  covering  with  hot  water.  Filter  into  an 
1  J.Ind.  Eng.  Ckem.,  4,  17. 


98  QUANTITATIVE  ANALYSIS 

Erlenmeyer  flask,  add  i  or  2  cc.  of  hydrogen  peroxide  and  boil 
for  five  minutes  to  destroy  the  excess.  Add  a  slight  excess  of 
nitric  acid,  shake  vigorously  to  remove  carbon  dioxide.  Trans- 
fer to  a  250  cc.  beaker,  and  add  2  cc.  dilute  (i  :  i)  nitric 
acid  for  each  100  cc.  of  solution.  Add  20  cc.  of  a  2o-per  cent 
solution  of  lead  nitrate  with  constant  stirring.  Filter  on 
asbestos,  wash  several  times  with  cold  water.  Transfer  the 
asbestos  mat  to  a  beaker  and  decompose  the  lead  chromate 
with  hot  dilute  (i  :  4)  hydrochloric  acid.  Cool  the  solution, 
dilute  to  200  cc.  and  titrate  with  standard  ferrous  sulphate 
solution,  using  potassium  ferricyanide  as  outside  indicator. 

Notes.  —  i.  The  principle  of  this  method  is  based  upon  the 
precipitation  in  boiling  solution  of  chromium  hydroxide,  in 
presence  of  ferrous  iron,  and  the  subsequent  oxidation  of 
chromium  to  chromate,  the  latter  being  measured  by  a  stand- 
ard ferrous  sulphate  solution. 

2.  Noyes  and  Bray1  have  studied  the  conditions  for  the 
separation  of  chromium  and  vanadium,  and  find  that  by  boil- 
ing with  barium  carbonate  all  of  the  chromium  is  precipitated, 
and  the  separation  from  vanadium  is  complete.    To  further 
insure  separation  Cain  separates  chromium  as  lead  chromate 
under    conditions    which    would    prevent    vanadium    being 
precipitated. 

3.  The  addition  of  hydrogen  peroxide  is  for  the  removal  of 
any  nitrite  which  if  present  might,   on  acidifying,   reduce 
chromium  or  vanadium.     The  excess  hydrogen  peroxide  must 
be  removed  as  it  would  reduce  chromic  acid. 

4.  The  removal  of  carbon  dioxide  is  simply  for  the  purpose 
of  getting  a  precipitate  which  will  settle  rapidly. 

DETERMINATION  OF  TUNGSTEN  IN  STEEL 

Weigh  2-5  grams  of  sample  into  a  porcelain  casserole  and 
dissolve  in  60  cc.  nitric  acid  (sp.  gr.  1.20)  with  the  addition, 
from  time  to  time,  of  a  few  drops  of  strong  hydrochloric  acid. 
If  the  precipitated  tungstic  acid  is  dark  colored,  digest  for 
some  time  with  occasional  addition  of  a  few  drops  of  hydro- 
chloric acid  until  the  precipitate  becomes  a  light  yellow. 
1  Tech.  Quart.  (1908),  21,  14. 


DETERMINATION  OF  TUNGSTEN  IN  STEEL  99 

Evaporate  the  solution  to  dryness  and  heat  to  decompose 
nitrates.  Moisten  with  concentrated  hydrochloric  acid  and 
evaporate  to  dryness.  Take  up  in  concentrated  hydro- 
chloric acid  and  warm  until  all  ferric  oxide  is  in  solution. 
Evaporate  off  the  excess  of  hydrochloric  acid,  and  continue 
until  the  solution  becomes  syrupy.  Dilute  with  50-75  cc.  of 
dilute  hydrochloric  acid,  stir,  allow  to  settle  and  filter.  Wash 
the  precipitate  on  to  the  filter  with  dilute  hydrochloric  acid 
(i:  5),  adding  some  paper  pulp  if  there  is  any  tendency  to 
pass  through  the  filter  paper;  and  complete  the  washing  with 
hydrochloric  acid.  Remove  any  tungs tic  oxide  adhering  to 
the  casserole  with  a  small  piece  of  filter  paper  moistened  with 
ammonia,  add  to  the  precipitate,  ignite  over  a  Tirrill  burner, 
at  first  at  a  low  temperature,  and  finally  at  full  heat. 

Treat  with  2-3  drops  of  sulphuric  acid  and  about  2-3  cc.  of 
hydrofluoric  acid,  evaporate  to  remove  silica,  and  ignite. 

Fuse  with  six  times  its  weight  of  sodium  carbonate,  allow 
to  cool,  digest  with  hot  water,  and  filter,  washing  the  residue 
with  hot  water.  Nearly  neutralize  the  filtrate  with  nitric 
acid,  boil  off  carbonic  acid,  allow  to  cool,  and  make  slightly 
acid  with  nitric  acid.  Add  mercurous  nitrate1  solution  to 
the  gently  boiling  solution,  allow  to  settle  and  test  with  more 
mercurous  nitrate.  Then  add  an  emulsion  of  mercuric  oxide 
and  water  until  excess  nitric  acid  is  neutralized.  Allow  the 
precipitate  to  settle,  filter,  wash  several  times  by  decantation, 
adding  a  few  drops  of  mercurous  nitrate  solution  to  the  hot 
water,  and  finally  wash  with  water. 

Dry  and  ignite  the  precipitate  in  a  porcelain  crucible  and 
weigh  as  WOs. 

Notes.  —  i.  Steels  containing  about  6  per  cent  of  tung- 
sten and  about  0.60  per  cent  of  carbon  are  extensively  used  in 
the  hardened  condition  for  permanent  magnets.  When  used 
for  electric  meters  they  are  seasoned,  after  hardening,  by  heat- 
ing for  a  long  time  at  100°.  Tools  for  making  finishing  cuts  at 

1  ioo  grams  of  salt  dissolved  in  one  liter  of  water,  to  which  some  free 
mercury  has  been  added. 


100  QUANTITATIVE  ANALYSIS 

relatively  high  speed  are  made  of  steels  .containing  i  per  cent 
of  carbon  and  3-4  per  cent  of  tungsten.  According  to  Arnold 
and  Read1  carbon  is  combined  with  iron  in  low  tungsten  steels, 
but  with  increasing  tungsten  more  of  the  carbon  enters  into 
combination  with  it  and  hi  steels  containing  11.5  per  cent  or 
more  all  of  the  carbon  is  in  combination  with  tungsten. 

High  speed  steels  contain  13-18  per  cent  of  tungsten, 
2.5-5.00  per  cent  of  chromium,  0.60-0.70  per  cent  of  carbon, 
and  usually  under  i.oo  per  cent  of  vanadium.  They  are 
characterized  by  their  ability  to  be  worked  at  a  speed  3-5 
times  greater  than  with  plain  carbon  steels,  and  to  maintain 
their  hardness  at  a  red  heat  ("red-hardness").  These  steels 
are  hardened  at  a  temperature,  white  heat,  which  would  ruin 
a  plain  carbon  steel.  It  is  believed  that  at  the  high  tempera- 
ture which  is  necessary  for  satisfactory  hardening,  double 
carbides2  of  chromium  and  tungsten  are  formed,  which  persist 
on  rapid  cooling,  and  also  to  some  extent  on  slow  cooling. 

2.  The  principle  of  this  method  is  dependent  upon  the  pre- 
cipitation of  tungstic  acid  anhydride,  WOg,  from  an  oxidizing 
acid   solution.     This   precipitate   is   subsequently   converted 
into  mercurous  tungstate,  ignited  and  weighed  as  WO3.3 

3.  If  the  residue  obtained  after  removal  of  silica  is  weighed, 
it  will  give  a  fairly  accurate  result  for  tungsten.     This  residue, 
however,  invariably  contains  traces  of  iron,  chromium,  and 
manganese,  and  it  is  the  purpose  of  the  fusion  with  sodium 
carbonate  to  remove  tungsten  as  soluble  sodium  tungstate 
from  the  elements. 

4.  In  ferro-tungsten  and  tungsten  metal,  insoluble  in  acid, 
decomposition  may  be  accomplished  by  fusing  the  powdered 
metal  with  a  mixture  of  sodium  carbonate  and  potassium 
nitrate,  or  with  Eschka4  mixture.     In  either  case  the  product 
is  soluble  sodium  tungstate  which  may  be  precipitated  as 
mercurous  tungstate  and  ignited  to  tungstic  acid. 

1  Proc.  Inst.  Mech.  Eng.  (1914),  223. 

1  Edwards,  /.  I.  and  S.  Inst.,  1908,  2,  104. 

1  WOs  begins  to  sublime  500°  below  its  m.p.  at  1473°  —  C.A.,  12,  226. 

«  See  page  48. 


DETERMINATION  OF  VANADIUM  IN  STEEL  IOI 

DETERMINATION  OF  VANADIUM  IN  STEEL 

Dissolve  a  2-gram  sample  in  20  cc.  of  hydrochloric  acid 
(sp.  gr.  i. 20)  adding  sufficient  nitric  acid  to  completely  oxidize 
the  iron.  Evaporate  to  small  volume,  and  in  case  tungstic 
acid  separates,  dilute,  filter,  wash  with  dilute  hydrochloric 
acid,  and  evaporate  the  filtrate  to  a  syrupy  consistency. 
Pour  the  solution  into  a  separatory  funnel,  and  wash  the 
casserole  free  from  ferric  chloride  by  successive  small  addi- 
tions of  hydrochloric  acid  (sp.  gr.  i.io),  taking  care  to  keep 
the  volume  small.  Add  an  equal  volume  of  ether,  and  shake 
for  several  minutes,  releasing  the  pressure  occasionally  by 
opening  the  stopcock  of  the  funnel,  holding  the  tube  of  the 
funnel  pointing  upward  and  allowing  time  for  any  ejected 
solution  to  return  into  the  bulb.  Draw  off  the  hydrochloric 
acid  solution  from  the  ether  layer  into  a  second  separatory 
funnel  and  repeat  the  shaking  with  ether. 

Again  separate  the  hydrochloric  acid  layer  from  the  ether, 
and  evaporate  to  small  volume.  Convert  the  hydrochloric 
acid  solution  into  a  nitric  acid  solution  by  several  evaporations 
to  small  volume  after  the  addition  of  some  concentrated 
nitric  acid  between  evaporations.  Dilute  slightly  with  water, 
add  two  or  three  drops  of  sulphurous  acid,  heat  to  boiling  and 
pour  slowly  into  100  cc.  of  boiling  sodium  hydroxide  solution 
(100  grams  per  liter).  Boil  a  few  minutes,  filter,  and  wash 
with  hot  water.  Acidify  the  filtrate  slightly  with  nitric  acid, 
make  slightly  alkaline  with  sodium  hydroxide  and  boil. 
Filter,  and  to  the  filtrate  add  10  cc.  of  a  solution  of  lead  ace- 
tate, and  then  enough  acetic  acid  to  give  a  decided  odor. 
Heat  to  boiling  and  filter  off  the  lead  vanadate  on  asbestos, 
washing  with  hot  water.  Dissolve  by  pouring  through  the 
precipitate  hot  dilute  hydrochloric  acid.  Evaporate  nearly 
to  dryness,  add  50  cc.  concentrated  hydrochloric  acid  and 
again  evaporate.  Add  10  cc.  concentrated  sulphuric  acid 
and  evaporate  until  the  acid  fumes  freely.  Cool,  dilute  to 


102  QUANTITATIVE  ANALYSIS 

150   cc.   and   titrate  with   dilute  potassium  permanganate, 
keeping  the  solution  at  a  temperature  of  60-70°. 

Notes.  —  i.  The  so-called  vanadium  steels  nearly  always 
contain  chromium  and  should  in  reality  be  called  chrome- 
vanadium  steels.  Many  plain  carbon  steels  have  been  treated 
with  vanadium,  and  some  of  them  contain  the  element  in  small 
amounts,  the  treated  metal  having  desirable  properties.  The 
amount  of  vanadium  contained  in  them  is  so  small  that  there 
is  no  more  reason  why  they  should  be  called  vanadium  steels 
than  the  ordinary  steel  should  be  called  manganese  steel  on 
account  of  its  having  been  treated  with  ferro-manganese. 
These  steels  probably  have  greater  fatigue  resisting  qualities 
than  plain  carbon  steels. 

Chrome-vanadium  steels  are  extensively  used  in  the  manu- 
facture of  automobiles  and  are  used  in  those  parts  where  it  is 
desirable  to  have  high  elastic  limit  and  at  the  same  time  high 
ductility.  Such  steels  contain  approximately  i.oo  per  cent 
of  chromium  and  0.20  per  cent  of  vanadium,  the  carbon 
content  varying,  depending  upon  the  use. 

Vanadium  is  frequently  used  in  high-speed  tool  steels  in 
amounts  varying  from  0.40  to  2.50  per  cent,  but  is  usually 
under  i.oo  per  cent.  The  steels  containing  vanadium  are 
supposed  to  have  superior  properties. 

2.  Advantage  is  taken  of  the  solubility  of  ferric  chloride 
in  ether  to  separate  most  of  the  iron  from  vanadium.  The 
remainder  of  the  iron,  chromium,  manganese,  nickel,  and 
copper  are  separated  by  means  of  sodium  hydroxide.  The 
vanadium  is  then  separated  as  lead  vanadate,  subsequently 
being  reduced  by  hydrochloric  acid  to  vanadyl  salt  and  then 
oxidized  in  sulphuric  acid  solution  with  potassium  perman- 
ganate to  vanadic  acid. 

The  essential  reactions  involved  are  the  following: 

Pb3(VO4)2  +  6HC1  =  3PbCl2  +  2H3VO4, 
2H3V04  +  6HC1  =  2VOC12  +  6H20  +  C12, 
VOC12  +  H2S04  =  VOSO4  +  2HC1 
ioVOSO4  +  2KMnO4  +  8H2S04  = 

SV202(S04)3  +  K2S04  +  2MnS04  +  8H2O. 


ANALYSIS    OF    DURALUMIN  103 

3.  The  Rothe1  separation  of  ferric  chloride  by  means  of 
ether  is  an  extremely  useful  process  and  may  be  applied  to  the 
separation  of  iron  from  chromium,  aluminum,  titanium,  nickel, 
and  manganese.  When  these  elements  are  present  in  relatively 
small  amounts,  it  serves  as  a  convenient  process  for  concen- 
trating them  from  the  larger  amount  of  iron. 

Molybdenum  chloride2  is  also  soluble  in  ether  and  in  a 
separation  will  be  found  with  the  ferric  chloride,  from  which  it 
may  be  separated  as  sulphide  by  precipitating  under  pressure 
with  hydrogen  sulphide.  It  may  then  be  converted  into  sul- 
phate, reduced  as  in  the  method  for  phosphorus,  and  titrated 
with  potassium  permanganate. 

4.'  It  is  necessary  to  convert  the  hydrochloric  acid  solution 
into  nitric  acid  solution  on  account  of  using  lead  acetate  as  a 
precipitant.  The  removal  of  one  volatile  acid  by  another  is  not 
a  question  of  the  strength  of  the  acid  removed,  but  one  of  vol- 
atility and  the  amount  of  acid  which  is  present  in  excess. 

Precautions  must  be  used  in  evaporating  nitric  acid  solu- 
tions containing  large  amounts  of  iron  as  hydrolyzed  products 
separate  which  are  soluble  only  in  hydrochloric  acid. 

5.  The  few  drops  of  sulphur  dioxide  are  to  reduce  any 
chromium  which  may  have  been  oxidized  to  chromate  ions, 
and  the  second  treatment  with  sodium  hydroxide  removes  all 
of  the  chromium  and  nickel. 

6.  Some  differences  of  opinion  has  been  expressed  as  to  the 
reduction  of  vanadium  by  means  of  hydrochloric  acid.     Cam- 
pagne3   has  obtained  satisfactory  results,  and  others  have 
verified  his  results.     Apparently  the  conditions  must  always 
be  the  same,  and  in  order  to  avoid  variations  some  workers 
prefer  reduction  with  sulphurous  acid. 

ANALYSIS   OF  DURALUMIN4 

DETERMINATION    OF    SILICON   AND    IRON 

Dissolve  one  gram  of  well  mixed  drillings  in  45  cc.  of  acid 
made  by  mixing  5  cc.  nitric  acid  (sp.  gr.  1.42),  10  cc.  hydro- 
chloric acid  (sp.  gr.  1.20),  5  cc.  sulphuric  acid  (sp.  gr.  1.84), 

1  Rothe,  Mittheilungen  Konig.  Tech.  Versuchs.  zu  Berlin,  1892. 

J  Blair,  J.  Am.  Chem.  Soc.,  30, 1228. 

1  Comptes  Rendus  (1903),  137,  570. 

*  Standard  Methods  of  Analysis  (modified),  Aluminum  Co.  of  America. 


104  QUANTITATIVE  ANALYSIS 

with  25  cc.  of  water,  using  a  casserole  provided  with  a  cover 
glass.  When  the  drillings  are  completely  dissolved,  evaporate 
the  solution  to  dryness  and  raise  the  heat  till  the  sulphuric 
acid  fumes  freely.  Continue  until  a  few  drops  have  fallen 
from  the  center  of  the  glass.  This  insures  the  freedom  of  the 
solution  from  hydrochloric  acid  and  nitric  acid,  and  the  com- 
plete dehydration  of  the  silica.  Take  up  the  residue  with  5  cc. 
of  concentrated  sulphuric  acid  and  about  100  cc.  of  water; 
boil  until  the  sulphate  is  completely  dissolved,  and  filter. 
Wash  the  residue  at  least  seven  times  with  hot  water  to 
remove  sulphates,  and  ignite  in  a  weighed  platinum  crucible. 
Weigh  the  ignited  crucible.  The  difference  between  -the  two 
weights  represents  the  silicon  as  silica.  Calculate  the  silica  to 
silicon. 

DETERMINATION    OF   IRON 

Pass  the  hot  nitrate  and  wash  water  from  the  silicon  deter- 
mination through  a  Jones  reductor,  following  the  procedure 
given  on  page  75  and  titrate  with  potassium  permanganate. 
The  Jones  reductor  should  have  been  prepared  for  service  by 
washing  with  definite  amounts  of  hot,  dilute  sulphuric  acid 
and  water/ and  the  solution  in  which  the  iron  is  to  be  deter- 
mined should  be  preceded  and  followed  by  hot  dilute  sul- 
phuric acid  as  directed  under  the  Determination  of  Phosphorus 
in  Iron  and  Steel. 

DETERMINATION    OF    COPPER   AND    MAGNESIUM 

Place  one  gram  of  the  alloy  together  with  5  grams  of  solid 
sodium  hydroxide  in  a  500  cc.  porcelain  casserole  and  add  just 
enough  water  to  cover;  when  violent  action  has  ceased,  dilute 
to  200-250  cc.  with  hot  water  and  boil  until  solution  is  com- 
plete. Filter  while  hot  and  wash  the  residue  until  free  from 
alkali.  The  aluminum  and  most  of  the  zinc  dissolve,  while 
the  other  metals  remain  in  the  metallic  state. 

Dissolve  the  residue  in  hydrochloric  acid  (i  :  i)  using  a  little 
nitric  acid  if  necessary.  Neutralize  with  ammonia,  make 


ANALYSIS    OF    DURALUMIN  105 

weakly  acid  with  hydrochloric  acid,  heat,  and  precipitate 
copper  with  hydrogen  sulphide.  Filter  and  wash.  Ignite 
the  precipitate  in  a  porcelain  crucible,  cool,  add  2  to  3  cc.  of 
concentrated  nitric  acid  and  heat  gently  until  all  the  copper 
is  in  solution.  Transfer  the  solution  to  a  250  cc.  wide  mouth 
Erlenmeyer  flask  containing  0.5  cc.  of  concentrated  sulphuric 
acid,  and  evaporate  to  complete  dryness.  Cool,  add  25  cc.  of 
12  per  cent  acetic  acid  and  heat  until  solution  of  sulphates  is 
completed.  Add  5  cc.  of  saturated  Na2HPO4  solution.  When 
cold  add  3  grams  of  potassium  iodide,  and  allow  to  stand  for 
ten  minutes. 

Titrate  the  free  iodine  with  sodium  thio-sulphate.  A  few 
drops  of  fresh  starch  solution  are  added  near  the  end  of  the 
titration. 

To  the  nitrate  from  the  hydrogen  sulphide  precipitation 
add  5  cc.  concentrated  hydrochloric  acid,  then  a  small  excess 
of  ammonia  and  precipitate  with  hydrogen  sulphide.  Filter 
and  wash  with  water  containing  a  little  ammonium  sulphide. 

Make  the  nitrate  faintly  acid  with  hydrochloric  acid  and 
boil  off  hydrogen  sulphide,  adding  a  little  ammonium  per- 
sulphate toward  the  latter  part  of  the  boiling  to  oxidize 
sulphur. 

Add  30  cc.  saturated  solution  of  microcosmic  salt  and  cool. 
Add  ammonia  drop  by  drop,  stirring  vigorously  to  make  the 
precipitate  crystalline.  Then  add  an  excess  of  strong  am- 
monia. Let  stand  .for  two  hours  in  ice  water.  Filter,  wash 
with  cool  water  containing  5  per  cent  of  strong  ammonia  and 
5  per  cent  ammonium  nitrate.  Ignite  until  completely  white. 
Weigh  as  Mg2P2O7. 

DETERMINATION    OF   MANGANESE 

Weigh  out  accurately  about  0.2  gram  of  the  sample  in  which 
the  manganese  is  to  be  determined.  Place  sample  in  a  150  cc. 
beaker  and  add  50  cc.  of  water,  10  cc.  of  nitric  acid  (sp.  gr. 
1.42),  and  10  cc.  sulphuric  acid  (sp.  gr.  1.84).  Heat  until 
solution  is  complete,  and  all  nitrous  fumes  driven  off.  Re- 


106  QUANTITATIVE  ANALYSIS 

move  from  source  of  heat,  cool,  add  50  cc.  water,  10  cc.  silver 
nitrate  solution  containing  0.003  gram  per  cc.  and  one  gram 
ammonium  persulphate  and  heat  gently  until  color  is  fully 
developed.  Cool  to  room  temperature  and  titrate  with  stand- 
ard sodium  arsenite  solution. 

i.  Duralumin1  is  an  alloy  of  aluminum  having  approxi- 
mately the  composition 

Per  cent 

Copper 3.75 

Magnesium o.  50 

Manganese o.  60-0. 70 

Aluminum Balance 

and  with  small  amounts  of  silicon  and  iron  which  the  alum- 
inum contained  as  impuritites.  It  can  readily  be  forged  and 
is  always  used  in  this  condition.  It  also  responds  to  heat 
treatment,  and  the  properties  can  be  materially  improved  by 
this  means.  If,  after  forging,  the  alloy  be  reheated  to  400°- 
500°  C.  and  quenched  in  water  its  physical  properties,  hard- 
ness, tensile  strength,  and  elongation,  will  be  about  the  same 
as  when  forged,  viz.;  tensile  strength  35,000  pounds  per 
square  inch,  and  10  per  cent  elongation  in  two  inches.  Almost 
immediately  it  begins  to  harden  and  strengthen  so  that  after 
about  four  days  the  strength  has  increased  to  55,000  pounds 
per  square  inch  and  the  elongation  to  15-20  per  cent.  This 
change  in  properties  which  is  known  as  "aging"  is  much 
accelerated  by  heating  to  ioo°-2oo°  C.  The  change  at  the 
higher  temperature  is  rapid,  so  that  after  a  certain  critical 
time  corresponding  to  maximum  physical  properties  a  pro- 
longation of  the  time  produces  an  annealing  effect. 

The  material  which  has  been  subjected  to  the  aging  effect 
may  have  its  strength  further  increased  by  cold  work. 

The  effect  of  aging  duralumin  may  be  explained  by  taking 
into  account  the  lowering  of  the  solubility  of  the  compound, 
CuAl2,  from  500°  to  room  temperature.  At  the  higher 
temperature  CuAl2  is  held  in  solid  solution  and  this  state  is 
maintained  at  the  ordinary  temperature  by  quenching,  but 
it  will  separate  out  if  slowly  cooled.  In  the  quenched  alloy 

1  Wilm,  Metallurgie  8,  225;   Circular,  Bureau  of  Standards,  No.  76. 


ANALYSIS    OF    DURALUMIN  107 

separation  of  CuAl2  takes  place  slowly  at  ordinary  temperature 
more  rapidly  on  heating  at  ioo°-2oo°,  and  maximum  hardness 
corresponds  closely  to  a  certain  average  size  of  particle  sepa- 
rated. 

Duralumin  in  the  hardened  condition  is  remarkably  resis- 
tant to  corrosion  which  is  very  important  in  view  of  its  ex- 
tended use  in  air-plane  construction. 

2.  The  method  of  analysis  is  applicable  not  alone  to  dur- 
alumin but  to  other  aluminum  alloys  as  well. 

The  solubility  of  aluminum  and  some  of  its  alloys  hi  simple 
acids  is  so  slow  that  special  mixtures  of  acids  are  used  to  accel- 
erate the  action. 

3.  Aluminum  may  contain  some  or  all  of  its  silicon  in  the 
graphitic  form  which  is  not  attacked  by  acids  nor  oxidized 
by  heat.     If  present,  the  siliceous  residue  must  be  treated 
with  hydrofluoric  and  sulphuric  acids,  heated,  and  the  brown 
insoluble  residue  weighed  as  graphitic  silicon. 

4.  The  determination  of  manganese  in  aluminum  alloys  is 
based  upon  its  oxidation  in  the  presence  of  silver  nitrate  to 
permanganic  acid  by  means  of  ammonium  persulphate,  the 
destruction  of  the  excess  of  the  latter  by  heat,  and  the  titration 
of  the  permanganic  acid  by  means  of  sodium  arsenite.    The 
calculations  are  based  upon  the  following  reaction: 

2HMnO4+5Na3AsO3+4HN03  = 


io8 


QUANTITATIVE  ANALYSIS 
LOGARITHMS  OF  NUMBERS 


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LOGARITHMS  OF  NUMBERS  IOQ 

LOGARITHMS  OF  NUMBERS   (Continued} 


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2 

7 

9 

XX 

14 

16 

tl 

112 


QUANTITATIVE  ANALYSIS 


INTERNATIONAL  ATOMIC  WEIGHTS,   1921. 


Sym- 
bol. 

Atomic 
Weight 

Sym- 
bol. 

Atomic 
Weight. 

Aluminum 

Al 

27    i 

Neodymium 

Nd 

Antimony  . 

Sb 

I  2O.  2 

Neon 

Ne 

Argon  

A 

39.88 

Nickel  

Ni 

58  68 

Arsenic  

As 

74.96 

Niton  (radium  emana 

Barium 

Ba 

X37  37 

tion) 

Nt 

Bismuth 

Bi 

209  o 

Nitrogen 

N 

Boron. 

B 

no 

Osmium. 

Os 

Bromine  
Cadmium  

Br 
Cd 

79-92 
112.40 

Oxygen  
Palladium  

0 
Pd 

iG.OO 

106  7 

Caesium  

Calcium 

Cs 
Ca 

132.81 
4°  07 

Phosphorus  
Platinum 

P 
Pt 

31-04 

Carbon     

c 

12    OO5 

Potassium 

K 

Cerium  

Ce 

140.25 

Praseodymium. 

Pr 

Chlorine  

Cl 

35.46 

Radium  

Ra 

226  o 

Chromium  

Cr 

52.0 

Rhodium  

Rh 

102  9 

Cobalt 

Co 

58  97 

Rubidium 

Rb 

gr    A? 

Columbium 

Cb 

93  r 

Ruthenium  . 

Ru 

Copper  

Cu 

63  .57 

Samarium  

Sa 

Dysprosium  
Erbium 

Dy 
Er 

162.5 
167  7 

Scandium  
Selenium 

Sc 
Se 

45-i 

Europium 

Eu 

52  o 

Silicon 

Si 

28  i 

Fluorine 

F 

19  o 

Silver   . 

Ag 

107  88 

Gadolinium  
Gallium  
Germanium.  :  
Glucinum 

Gd 
Ga 
Ge 
Gl 

57-3 
70.1 

72.5 
9  J 

Sodium  
Strontium  
Sulphur  

Na 
Sr 
S 
Ta 

23.00 
87.63 
32.06 
181  5 

Gold  

Helium 

Au 
He 

97-2 
4  oo 

Tellurium  
Terbium. 

Te 
Tb 

127-5 

ICQ    2 

Holmium  

Ho 

63  5 

Thallium. 

Tl 

H 

i  008 

Th 

2?2    l*i 

Indium  

In 

14.8 

Thulium  

Tm 

Iodine 

I 

2'6  92 

Sn 

Il8    7 

Iridium  
Iron 

Ir 
Fe 

93-i 
55  84 

Titanium  
Tungsten 

Ti 
W 

48.1 

184  o 

Krypton  . 

Kr 

82  92 

Uranium 

u 

2*8    2 

Lanthanum  
Lead  
Lithium  

La 
Pb 
Li 

39-o 

07  .20 

6  .94 

Vanadium  
Xenon  
Ytterbium    (Neoytter- 

V 
Xe 

51-0 
130.2 

Lutecium  

Lu 

75  -° 

bium)  

Yb 

173.5 

Magnesium  

Mg 

24.32 

Yttrium  

Yt 

89.33 

Manganese.  .  . 

Mn 

54  93 

Zinc. 

Zn 

65  37 

Mercury  

Hg 

oo  6 

Zirconium 

Zr 

90.6 

Molybdenum  

Mo 

96.0 

INDEX 

PAGE 

Alkalies,  determination  of  in  silicate 9 

Allen  and  Bishop,  method  for  available  sulphur  in  pyrite 31 

Ash,  determination  in  coal 47 

Atomic  weights 112 

Bamber,  method  for  sulphur 87 

Barba,  method  for  chromium 94 

Barneby  and  Isham,  method  for  titanium  in  iron  ore 42 

Basic  acetate  method 16 

Brunck,  method  for  nickel 92 

Calcium,  determination  in  iron  ore '. 18 

Carbon,  apparatus,  for 57 

determination  in  steel 59 

forms  and  effects  upon  physical  properties 61 

Carbon-iron  equilibrium  diagram 63 

Chromium,  determination  in  chrome-vanadium  steel 97 

determination  in  steel 95 

Coal,  analysis  of 47 

determination  of  ash  in 47 

determination  of  moisture  in 47 

determination  of  sulphur  in  48 

determination  of  volatile  matter  in : 48 

Copper,  determination  in  bronze 54 

determination  in  duralumin 104 

determination  in  steel 91 

volumetric  determination  in  ore 43 

Di-methyl  glyoxime  method  for  nickel 92 

Drown,  method  for  silicon  in  iron 89 

Duralumin,  analysis  of 103 

Feldspar,  decomposition  by  means  of  sodium  carbonate 5 

determination  of  silica  in 5 

determination  of  alkalies  in 9 

Fresenius,  method  for  total  sulphur 32 

Gooch,  method  for  titanium 39 

Graphite,  determination  in  cast  iron 61 

"3 


1 14  INDEX 

PAGE 

Handy,  method  for  phosphorus  in  steel 82 

Iodine,  standardization  of  solution 83 

Iron,  determination  in  duralumin 104 

determination  in  spathic  iron  ore 20 

standard  for  potassium  permanganate 75 

Laumontite,  determination  of  silica  in 4 

Lead,  determination  in  bronze 54 

Logarithms 108 

Low,  A.  H.,  iodimetric  method  for  copper 43 

Lunge,  method  for  available  sulphur  in  pyrite 29 

Magnesium,  determination  in  iron  ore 18 

determination  in  duralumin 104 

Manganese,  determination  in  duralumin 105 

determination  in  steel 65,  69,  72 

gravimetric  determination  in  iron  ore 17 

Moisture,  determination  in  coal 47 

Nickel,  determination  in  steel 92 

Phosphor  bronze,  analysis  of 50 

Phosphorus,  alkalimetric  method 82 

determination  in  bronze 57 

determination  in  steel 75 

ferric  alum  method 77 

reductor  method 75 

Potassium,  determination  in  feldspar 9 

determination  as  perchlorate 13 

permanganate  solution,  standardization  of 20,  21 

permanganate,  standardization  in  Volhard  method 65 

Sampling i 

Silica,  determination  in  decomposable  silicate 4 

determination  in  refractory  silicate 5 

determination  in  spathic  iron  ore 15 

dehydration  of  in  silicates 4 

ignition  of i 5 

testing  the  purity  of 5 

Silicate,  determination  of  alkalies  in 9 

Silicon,  determination  in  cast  iron 89 

determination  in  duralumin 103 

Smith,  J.  L.,  determination  of  alkalies  in  silicate 9 

Sodium,  determination  in  feldspar 9 

oxalate,  standard  for  potassium  permanganate 21 


INDEX  115 

PAGE 

Sodium,  peroxide  method  for  sulphur  in  pyrite 33 

thiosulphate,  standardization  of 43 

Spathic  iron  ore,  analysis  of 15 

determination  of  calcium  in 18 

determination  of  iron  in 20 

determination  of  magnesium  in 18 

determination  of  manganese  in 17 

determination  of  oxides  of  iron  and  alumina  in 19 

determination  of  silica  in 15 

Sulphur,  determination  in  cast  iron 87 

determination  in  steel  by  evolution  method 83 

determination  in  pyrite 29,  31,  32 

evolution  method 83 

gravimetric  method  in  cast  iron 87 

Tin,  determination  in  bronze 50 

Titanium,  determination  in  iron  ore 39 

Tungsten,  determination  in  steel 98 

Vanadium,  determination  in  steel 101 

Volatile  matter,  determination  in  coal 48 

Volhard  method  for  manganese 65 

Williams  method  for  manganese 69 

Zimmermann-Reinhardt  method  for  iron 20 


UNIVERSITY  OF  CALIFORNIA  AT  LOS  ANGELES 

THE  UNIVERSITY  LIBRARY 
This  book  is  DUE  on  the  last  date  stamped  below 


2S  19!  i* 


feft  '  « 


12  193F 

21    t99S 


1        1935 


idaet 

DEC  3      1935 

£)G  i      * 

4-  J937 


29 

.""i6?  W38 

Form  L-9-157n-3,'34 


MOV 

APR  5  -  195b 
SEP  18  195* 


QD 

101 

F29 


Pay    - 

crmrse    in 


quantitative 


analysis. 


